just say the answer, Sonny substituted 5 for x in the proportion StartFraction 16 over x EndFraction = StartFraction 48 over 15 EndFraction and cross multiplied to get 240 = 240. Why is this? because the cross sums of the proportion are equal because the cross differences of the proportion are equal, because the cross products of the proportion are equal, because the cross quotients of the proportion are equal