So the equation looks like this : 15*3x=78
subtract 15 from both sides: -15 -15
then divide by 3 from both sides
to isolate the variable: 3x=63
3/3x=63/3
x=21 (your mystery number is 21)
He doesn't have a positive number. Add $45 and $112 together and it exceeds $79
we have

we know that

therefore
<u>the answer is</u>
The expression equivalent is 