B. Solve the missing values as indicated.
1. If y varies directly as x, and y = 21 when x = 7, find y when x = 16.
2. If m varies inversely as n, and m = 12 when n = 5, find m when n = 4.
3. If r varies directly as the square of s, and r = 108 when s =
6, find r when
s = 7.​