First, set up 2 equations, one for each service, using w for weight. (I'm using x for the first service, and y for the second one)
x=5+0.25w
y=2+0.35w
Since the prices (x and y) end up being the same, we can set the equations equal to each other:
5+0.25w=2+0.35w
Now, we can simplify and solve for w, the weight.
3=0.1w
30=w
So, his package weighs 30 ounces.