Question

Can someone please tell what is f(5)

Answer 1

f(5). 5 is being multiplied by f. Now there are 2 ways you could do this.
1. f(5) = 5 * f = 5f
2. you could substitute the variable for a number. Usually, in this case, the number needed to substitute f is already in the problem. Sometimes however, you have to make up the number.