book Maths Puzzle Numerical Ability

Simplify the expression

(-3a^-3 b^7 / 2a^4 b^2)^3

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book Other Question

In the first NFL championship played in 1967, Green Bay and Kansas City scored a total of 45 points. Green Bay won by 25 points. What was the score? Sorry if the subject is wrong!

My question is:

3x-y= -3/2
4x+y=5

My work:

4x+y=5
-4x -4x

From there I get really confused! Thanks for the help!