What is the potential at a point that is 25% of the way from one particle to the other?

What is the potential at a point that is 25% of the way from one particle to the other?

The electric potential at a point that is halfway between two identical charged particles is 450 V.

I think I use V= k q/r but i don’t know what number to use for q or where to go from there.

The potential at the midpoint is 2*k*q/(r/2) = 4*[k*q/r] =450

so k*q/r = 450/4 = 112.5

now we have V = k*q/(3r/4) + k*q/(r/4) = 4*k*q/3r + 4*k*q/r = 16*k*q/3r = 16/3*k*q/r

so new V = 16/3*112.5 = 600V

What is the potential at a point that is 25% of the way from one particle to the other?