Please Help! This is so hard!

https://en.wikipedia.org/wiki/Coin_problem

According to wikipedia: "With only 2 pence and 5 pence coins, one cannot make 3 pence, but one can make any higher integral amount."

So the answer is three..?

3 pence. It's impossible to make 3 pence with 4 and 5 pence stamps.

Actually, it's 11 pence.

11=4+4+3

numbers greater than 11 can be made with 4x+5y; x, y>0