1 fish=10 points
Since He catches 2 fishes, then;
2 fishes= 2 x 10 = 20 points
Crabs = -5 points
Since he catches 4 crabs, then
4 crabs = - 5 x 4 = -20 points
Her point is
20 points - 20points = 0
If we are to write as an equation, we will have;
10 x - 5y
where x is the number of fishes catch and y is the numberb of crab catch
Then from the question, he catches 2 fish, which means x = 2 and he catches 4 crabs, which means y=4
substituting into the ; 10x - 5y
10(2) - 5(4) = 0