In one hour, hairdressers are charged with $20 for rent, and since haircuts cost $10, the minimum number of haircuts a hairdresser should give per hour to earn money is three hours. This is shows that the hairdressers would be able to earn $10 per hour.
Let us make an equation to solve : Y=mx+b (general form of a linear equation) y=10x-20 (x is the number of haircuts,y is the amount she earns) the minimum amount to carry out all the expenses is $20 so, 20=10x-20 20+20=10x 40=10x 40/10=x 4=x so she must do 4 haircuts in an hour