I like to use variables that refer to the first letter of the quantity they represent.
The amount of money Waldo has if he has $10 more than Joe
I would think of this as Waldo's money (W) is (=) $10 more (10 +) than Joe (J).
So W = 10 + J.
How much weight Kirk can lift if he lifts 30 lbs more than his brother.
Think of this as Kirk's weight (K) is (=) 30 lbs more (30 +) than his brother (B).
So K = 30 + B.
Here's one for you to do:
Now Josh knows two more things than the substitute. :)
Hope this helps,
Stephen La Rocque.