Harry has 9 points.
First, make some expressions to show what you know. I'll use the variables b, h, and n to represent the number of points each player has
h = b/2
n = h - 5
b + h + n = 31
Substitute h - 5 for n in the 3rd expression
b + h + h - 5 = 31
Now substitute b/2 for the h's in that expression
b + b/2 + b/2 - 5 = 31
Now solve for b, first add the b terms together
2b - 5 = 31
Add 5 to both sides
2b = 36
Divide both sides by 2
b = 18
We now know that Butch has 18 points, so plug that value into the formula for Harry's points
h = b/2
h = 18 / 2
h = 9
And we now know that Harry has 9 points.
