r varies jointly as s and t. Given two sets of values below, find the missing value.

First set: r = 12, s = 8, t = 4

Second set: r = ?, s = 8, t = 4

q varies jointly as r and s. Given two sets of values below, find the missing value.

First set: q = 1.2, r = 0.3, s = 0.4

Second set: q = ?, r = 1.8, s = 0.2

a varies jointly as b, c, and d. Given two sets of values below, find the missing value.

First set: a = 24, b = 4, c = 8, d = 3

Second set: a = ?, b = 6, c = 14, d = 4

m varies directly as n and inversely as p. Given two sets of values below, find the missing value.

First set: m = 10, n = 4, p = 8

Second set: m = ?, n = 20, p = 40

p varies directly as q and inversely as r. Given two sets of values below, find the missing value.

First set: p = 0.6, q = 6, r = 5

Second set: p = ?, q = 18, r = 2

A varies jointly as b and c and inversely as d. Given the two sets of values below, find the missing value.

First set: A = 0.645,b = 5, c = 6, d = 7

Second set: A = ?, b = 16, c = 6, d = 4