In order to solve this equation we will need to use what we know in order to find the answer.
If Huge ate 5/8's of the pizza and 8/8's creates a whole pizza then the question is quite simple. There is only 1/8's remaining after the boys finish their meal but 5/8's of the pizza was already eaten by Hugo meaning Lucas has to eat 2/8's of the pizza in order for there to be only 1/8's of the pizza left which means 2/8's is your answer.
The sum must be larger (not equal to) the longest side. If it's exactly the same, there's no room to for the shorter two sides to angle up to form a triangle.