What is the potential halfway between two point charges spaced 1 mm apart if q1=10 micro coulombs and q2= -5 micro coulombs?

Question

Attempt at solution:
no idea but need to get this right our homework is graded

Answer 1

distance to each charge is .0005m

Voltage is scalar, so they add.

V=k(10micro/.0005 -5micro/.0005)=k*5micro/.0005