Remark
None of them are correct.
Solve
9/10 = z/9 Since 9 is smaller than 10 (both in the denominator), the answer(z) should be smaller than the nine in the numerator. That means that the second and third answers are incorrect. To find z, multiply both sides by 9
(9/10) * 9 = (z/9)*9
9/10 * 9 = z
9*9/10 = z
81/10 = z
z = 8.1
the last one is the closest, but there is no real answer.
