Help me solve this ,would you?

34

You sure?

that would be 45

f(1,4)=5
f(2,5)=12
f(3,6)=21
f(5,8)=a
solve for a
=> f(a,b)=a * b+a
f(5,8)=5 * 8+5=45
answer: 45

The answer is 45

It is a wrong answer

Make sense

45 :D