Resistors in series

[mustang]

Problem 7.
A(n) 5.0 ohm resistor is connected in series with another resistor and a 6.0 V battery. The current in the circuit is 0.64A.
Calculate the value of the unkonwn resistance. Answer in ohms.
Note: I don't how to slove this problem.

Problem 11.
A 6.0V battery is connected to four resitors, 8.1ohm, 6.5ohm, 4.0ohm, 6.1ohm. Calculate the current in the 6.1 ohm resistor. Answer in A.

Problem 13.
A(n) 3.2 ohm resistor, a(n) 7.0 ohm resistor, and a(n) 14.1 ohm resistor are connected in parallel across a 24.0 V battery.
What is the current in the 3.2 ohm resistor? Answer in A.

[chroot]

Start with problem 7. When you wire resistors in series, their resistances add. Thus the total resistance in the circuit is 5 + R ohms, where R is the unknown resistance. Ohm's law indicates the total current in the circuit must be 6.0 V / (5 + R) ohms = 0.64 A.

Solve for R.

- Warren