Setting up formulas, algebra how to? Help needed tonight, please

[Saturnfirefly]

Homework Statement

A:
1
To play tennis at the local tennis club costs 150 kr/hour for non-members and 90 kr/hour for members. A membership costs 2100 kr a year. How many hous of tennis does one have to play to make it wothwhile to be a member? (kr is the swedish currency)

2
In a factory, goods are packed in both large and small boxes. The total mass of 3 large and 7 small boxes is 48.3 kg. The total mass of 4 large and 5 small boxes is 46.2 kg. Find the mass of each type of box.

B:
1
The final bill for a recent party was $400. There were two guests of hounour who did not pay anything so the cost was spread equally amongst the rest. If tehy each paid $10 mor than they would otherwise have done, how many were at the party altogether?

2
A shopkeeper has two brands of coffe, A at the price 13.50 kr/kg and B at 10.50 kr/kg. He wants to make a 50 kg mixture of these two, that can be sold for 11.30 kr/kg. How much of each brand shall he take? (simultaneous equation)

3. Evariste bought n oranges for 70p. Later he bough (n+1) apples for 60p. Each orange costs 4p more than each apple. Find n.

4. Two consecutive positive even numbers are squared and added together. The answer is 340. Find the two numbers.

Homework Equations

The Attempt at a Solution

I'm having some problems with setting up formulas... I just don't understand how I'm supposed to. I can't do it at all. Please tell me how to do it easy. :) Thank you!
Pleasee... at least one from a and one from b... it really means a lot to me.

 

[symbolipoint]

For A2 and B2, you need two unknowns and you will derive two equations (for each exercise). For the large and small boxes exercise, say x=mass of small box, y=mass of large box. The rest of this problem is just simple translation.

 

[dlgoff]

Hint for 1A. First you know you are going to be a member. So what operation do you need to do with the membership cost and the hourly rate inorder to get an answer in units of hours?

 

[berkeman]

I'm having some problems with setting up formulas... I just don't understand how I'm supposed to. I can't do it at all. Please tell me how to do it easy. :) Thank you!
Pleasee... at least one from a and one from b... it really means a lot to me.

You know that we will not provide you with the answers. In your other threads, you showed your work and were told where you were making mistakes. You must show your work here as well.