z = (a*sqrt(x)) / ( b*y^2)
now 135 = (a*sqrt(49) / (b*8^2) = (a*7) / (b*64) -> 135 = (7/64) * (a/b) -> a/b = (135*64) / 7
next comes z = (a*sqrt(36)) / (b*3^2) -> z = (a/b) * (6/9)
now put (a/b) in and you get z = (135*64*6) / (7*9) = 51840 / 63 = 822.857... ie 822.86
hope i didn't make a mistake in the calculations