exam Maths Puzzle Numerical Ability

This is a last Subsitution question, but this one says solve by either ;addition or subtraction.

The problem is:
12a-5b=18
15a-5b=30

Please and Thank You=)

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exam Other Question

I HOPE U CAN HELP ME WITH THIS....SOLVE THE EQUATION AND INEQUALITIES. WRITE THE SOLUTION TO THE INEQUALITIES IN INTERVAL NOTATION. THANK U.

A) 2|3-P|-4=2

B) 2|3-P|-4<2 How do you figure this out when y is isolated on both equations:
y=3x+1
y=6x-1

Thank you