Three more than a number is -5. How do you find the number?
Examples like these are the first steps in learning how to solve problems by making and and solving an algebraic equation.
"Three more than" means 3 added to some number.
In this case, let "the number" be
"Three more than a number" is written as
"is -5" tells us the answer. It means something
Put all this together ....
Subtract 3 from both sides