7.
irt = simple Interest we can fill in what we know so $500 * I * 20 = $250 than we solve for I so $250 / 500 = 0.5 than 0.5 / 20 = 0.025
8. Irt = simple interest fill it in 850 * I * 10 = $255 and then solve for I 255 / 850 = 0.3 than 0.3 / 10 = 0.03
9. Irt = simple interest 1200 * I * 15 = $720 and than solve for I so 720 / 1200 = 0.6 and then 0.6 / 15 = 0.04