book Maths Puzzle Numerical Ability

Use a system of equations to solve the following:

The sum of two numbers is 54. The difference of the two numbers is 18. Find the two numbers.

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book Other Question

Solve by addition state if it is inconsistent or dependent
1/3x - 1/2y = 5/6

1/2x - 2/5y = 9/10

I don't know where to begin on this problem.
express as a single logarithm

log(x^2+2x-3/x^2-4)-log(x^2+7x+6/x+2)

Thank you so much for all your help.