remember, you can do anything to an equation as long as you do it to both sides
but, for inequalities, if you multiply or divide both sides by a negative, you flip the sign
70+5x<30+15x
minus 5x both sides
70<30+10x
minus 30 both sides
40<10x
divide both sides by 10
4<x
x>4 is the solution set
a real world problem could be
company A charges a flat rate of $70 dollars to rent their car and also charge a rate of $5 per mile driven
company B charges a flat rate of $30 dollars to rent the car and also charge $15 per mile
how many miles do you have to drive for you to pay more for company B than A?