Question

A first number plus twice a second number is 24. twice the first number plus the second totals 21. find the numbers.

Answer 1

We do like the following:
Set the first number is a and the second is b.
We have two equations: a+2xb=24, 2xa+b=21
And we have 2xa+4xb=48 or 2xa=48-4xb
So: 48-4xb+b=21 or -3xb=21-48=-27 and we got b=-27:(-3)=9 and a= 6
a=6 and b=9