Answer :
If I get properly what you mean, it's about exchanging the letters (variables) with the numbers they are representing.
T = 5
H = 9
P = 6T + 4H
P = 6 * 5 + 4 * 9
P = 30 + 36
P = 66
T = 5
H = 9
P = 6T + 4H
P = 6 * 5 + 4 * 9
P = 30 + 36
P = 66