Bjorn is holding a tennis ball outside a second floor window (3.5 meters from the ground) and billie jean is holding one outside a third floor window (6.25 meters from the ground) how much more GPE does billie jean's tennis ball have? (each tennis ball has a mass of 0.06 kg)

The answer is 1.01 x 10^ (-11) N. I arrived to this answer through calculating the GPEs of both balls. Bjorn's ball has a GPE of 1.402 x 10^ (-11) N. Billie Jean's ball has a GPE of 2.503 x 10^ (-11) N. I subtracted the two and I found that Billie Jean's tennis ball has a GPE of 1.01 x 10^ (-11) more than Bjorn's tennis ball.