Question

A small sphere of mass m=.0064kg and charge q1= +28.9 nC is attached to the end of a string and hangs vertically. A second charge of equal mass and charge q2= -58nC is located below the first charge by a distance d= 2.00cm.

a. Find the Tension in the string

b. If the string has a maximum tension of .180 N what is the smallest value d can have in cm before the string breaks?

My answers: a. .063 N b. 59cm
are wrong and i don't know why.