Since you have y alone on one side of the equation......
Use substitution and plug in 1/2x-4 for y in the other equation.

Distribute

Combine like terms

Add 8 to both sides

Divide by 4
and 
Plug this value in for x

Simplify

Multiply everything by 8 and simplify

Divide.....

Your answers are:

Answer:
15x^2-x-2
Step-by-step explanation:
that's you're answer
This is the answer 9(-4-3) = -63
Answer:
Josh had $500
Karen had $100
Step-by-step explanation:
J = 5K
J - 20 = 6(K - 20)
5K - 20 = 6K - 120
100 = K
J = 500