how do yo solve linear equations

Well, my math teacher told me to use the formula y=mx+b with + b being your y-intercept, mx being your constant or slope, and y = being your answer. EX: Sam is a babysitter who charges a fee of $15 and $5 per hour, how much would she get if she worked for 2 hours.+b would be 15 and m would be 5 and x is 2 and if you solve it would be $25.