Question

One number is 9 less than three times a second number. If the first number plus twice the second number is 16, find the two number?

Answer 1

Say x = number 1
y = number 2
x = 3y - 9
x + 2y = 16
You're trying to find y, so, change the equations a bit.
x = 16 - 2y
Then you can plug this x value into the other equation, and you get
16 - 2y = 3y - 9
Combine these
5y = 25

y = 5

That make sense?

Answer 2

Nicely illustrated. Thanks a lot champ