At which point or points is the electric field zero in figure?

Question

I can not post the picture, but this is what it looks like:

1 2 3 4(4+)5 6(-)7 8 9 10

The (4+) is a proton with 4 charges.
The (-) is an electron with 1 charge.
They are on a number line 1-10.
The proton is between 4&5.
The electron is between 6&7.

I do not know how to start this question, or what to look at.

Answer 1

where is the force on a + test charge = to zero. Has to be right of the electron.

E=kq/r^2
put the test charge at p, to the right of the electron,

E=k(4q)/(p-4.5)^2-kq/(p-6.5)^2 if E is zero, then

4/(p-4.5)^2=1/(p-6.5)^2

now solve for p

Answer 2

Do you cross multiply the fractions?

I got 3p^2-43p=148.75

Is this right?

Answer 3

yes, "cross multipy). I didn't check your math, looks right. Now write in in satandard quadratic form, and solve for p with the quadratic equation

Answer 4

The answer for Part (a) is 6
For part (b) its 9