Charge of q5 in Electric Field Map with q4 and q6

[END]

Homework Statement

The electric field map is shown below. (Take it to be a self-consistent scale drawing at a particular moment in time.)

where \mathrm{q}_4 = +10 C, \mathrm{q}_6 = +10 C

What is the charge of \mathrm{q}_5 ?

Homework Equations

The Attempt at a Solution

I've tried the following values for \mathrm{q}_5:

$$-5,-10,-15,-20$$

and none of them are correct according to the online homework software. How would I find the charge of \mathrm{q}_5?

Thank you,

 

[BvU]

It looks as if halfway q₄ and q₅ the field is parallel to the axis at small distances x from the axis.
Write down the three contributions $\perp$ to the axis and make sure they cancel to first order in x.

And I wonder if three seemingly random shots at the answer counts as an attempt at solution :)
(If you have unlimited tries, step from -10 to -20 in very small steps ! ;) )

 

[DEvens]

What do you suppose it means that the drawing is "a self-consistent scale drawing"? What will that mean with regard to the field lines?

It's not too often that a physics problem can be solved by a Sesame Street character. "Ten! Ten field lines! Heh! Heh! Heh!"

 

[BvU]

I love it! Wish I had thought of that ... :D

 

[END]

Thank you for your replies!

You were right; each field line represents an equal fraction of the original charge. The answer came out to around $$-7.1 \mathrm{C}$$.