18. s = 5r^2 + 7......making r the subject s - 7 = 5r^2 (s - 7) / 5 = r^2...by taking the sqrt of both sides, it eliminates the ^2 ( sqrt (s-7)/5) = r
19. h = ut - 1/2gt^2....u = 100, t = 1 4/5(or 9/5)...g = 6.4 h = (100)(9/5) - 1/2(6.4)(9/5^2) h = 180 - 1/2(6.4)(3.24) h = 180 - 3.2(3.24) h = 180 - 10.368 h = 169.632 or 169 79/125
