James = 119 points
Sarah = 357 points
Roberts = 51 points
Step-by-step explanation:
Given that :
James = x points
Sarah = 3x points
Roberts = x - 68 points
Each point = 3 pence
All students have a total of £15.81
1 pound = 100 pence
£15.81 pound = 1581 pence
3x + 3(3x) + 3(x - 68) = 1581
3x + 9x + 3x - 204 = 1581
15x - 204 = 1581
15x = 1581 + 204
15x = 1785
x = 1785 / 15
x = 119
Hence,
James = 119 points
Sarah = 119 * 3 = 357 points
Roberts = 119 - 68 = 51 points