Two sandwiches and a juice cost £3.40. Four sandwiches and three juices cost £7.20. What is the cost of a juice?
2s + j = 3.4 and 4s + 3j = 7.2.
Creating a common multiple of s gives 4s + 2j = 6.8 and 4s + 3j = 7.2.
Elimination of s gives j = 0.4, or 40p.