Answer:
Sam: $30; Bethan: $24
Step-by-step explanation:
Since the ratio is 5:4 Sam has to pay 5/9 of the total which is 54. To find how much he pays set up the equation like this.

Cross Multiply
54(5)=9x
270=9x
Divide by 9
30=x
So Sam pays $30. To find out how much Bethan pays simply subtract 30 from 54
54-30=24
So Bethan pays $24
Convert to base 10
2×3² + 0×3¹ + 1×3^0 = 18 + 0 +1 = 19 base 10
so convert 19 to base 8
19 base 10 = 23 base 8
D is your answer