exam Maths Puzzle Numerical Ability

Simplify:

5(2a + b) - (a + 3b)

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exam Other Question

Could anyone help explain how to figure out the following problem?
3 + _7__
n
Thank you how do you do this problem:
-4x+5y+-11
2x+3y=11

The answer in the book is(4,1), and I do not understand how to get that.
Can you please explain?

Thank you!