Final answer:
a) The total cost of Gavin's drinks is £10.00. b) Lian should receive £3.50 in change.
Step-by-step explanation:
a) Gavin pays for one extra small drink and three large drinks. To find the total cost, we add the cost of each drink. The extra small drink costs £1.00.
Each large drink costs £3.00. Adding these values together, the total cost is £1.00 + (£3.00 * 3) = £1.00 + £9.00 = £10.00.
b) Lian pays for one small drink, one medium drink, and one extra large drink. To find the total cost, we add the cost of each drink. The small drink costs £1.50. The medium drink costs £2.00.
The extra large drink costs £3.00. Adding these values together, the total cost is £1.50 + £2.00 + £3.00 = £6.50.