Real world equation that can be modeled by the equation y=1/20x

Nick has to pay 5 cents in tax (5%) for every dollar he spends buying pizza. How much money does he have to pay in tax? Since 5=1/20*100, that means that if x is the amount of dollars he spends buying pizza, he has to divide that by 20 to get 5% of that amount and therefore the amount of tax he has to pay