Ok so 5 is t
You put 5 were the t is. Then answer the problem, then you find the function g and f. Then you multiply them together.
g(5)=5^2-5(5)
f(5)=2(5)+4
g(5)=25-25
f(5)=10+4
G times F
0 times 14 which equals 0
Hopefully this is the method your learning.