Consider a line of charges, q1 = 8.0 micro C at the orginin, q2 = -12 micro C at 2.0 cm, and q3 = 10 micro C at 4.0cm. What is the force on q3 due to the ohter two charges?

So you find F31 and u find the F32 and then add up the two forces to find your answer. But to find F31 they used a distance of .04m which confuses me. If the charges are as follows:

(q1)---(q2)-------(q3)

.02m .04m

Why wouldn't the distance from q1 to q3 be .06m?

Thanks.