Explanation:
D is directly proportional to x. D=36 when x=5. Work out the value of D when x=8.
Because they are directly proportional:
x/D = x/D
5/36 = 8/D
multiply both sides by D:
D(5/36) = D(8/D)
5D/36 = 8
multiply both sides by 36:
36(5D/36) = 8 * 36
5D = 288
divide both sides by 5:
5D/5 = 288/5
D = 288/5
or D = 57.6