book Maths Puzzle Numerical Ability

The sum of two numbers is 21. When the larger number is subtracted from four times the smaller number, the difference is 4. What are the two numbers?

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book Other Question

Find the coordinates of the midpoint of a segment with each pair of endpoints.
K(1/4, 1), L(1/8, 0)
I am unclear as how to do this thanks for any help.
Graph the solution set of x < -4.