The formula for calculating the cost in pounds (C) of a quarterly gas bill is C= 0.06n + 7.5, where n is the number of units of gas used.

a) What is the fixed cost er quarter charged by the gas supplier?
b) What is the cost per unit?
c) José uses 760 units of gas. How much will he have to pay?
d) Rearrange the formula to make n the subject.
e) Tracy's gas bill is £40.50. How many units of gas did she use?