Help needed with physics problem

Question

What is the net electric force on charge B in the figure? Suppose that a = 1.6 cm and b = 0.60 cm.

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A | (+) 1.0 nC

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| a

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B | (-) -2.0 nC

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| b

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C| (+) 2.0 nC

(Express your answer to two significant figures and include the appropriate units. Enter negative value if the force is directed downward and positive value if the force is directed upward.)

My previous answers, 0.0011, -1.07 x 10^33, -1.07 x 10^29, -1.07 x 10^-3, and -1 x 10^-7, are all incorrect

i only have one attempt remaining for this problem and my new answer is 9.3 x 10^-4. I want to check and make sure i got it right this time, before submitting

Answer 1

There are two attractive forces being applied to B in opposite directions. The upward force has magnitude

k(10^-9)(2·10^-9)/0.016²

(Notice that I have converted nC to coulombs, and cm to meters. k is Coulomb's constant, roughly 8.99x10⁹ in SI units.)

and the downward force has magnitude

k(2·10^-9)(2·10^-9)/0.006²

If we subtract these quantities and compute them, we get a downward net force of about 9.3·10^-4. Your answer is almost correct, but is missing a negative sign to indicate the downward direction.

It makes sense that the net force be downward anyway; charge C is both stronger and closer than charge A.