It is clearly stated that the total cost would be the same regardless of whether they choose Gold membership or Silver membership.
Let the number of times the equipment is hired = ‘N’
For Gold membership, total cost would be = £100 + (0.50N)
For Silver membership, total cost would be = £80 + (1N)
100 + 0.5N = 80 + 1N
20 = 0.5N
N = 40 times
Total cost for either Gold or Silver membership = 80 + 40 = £120
If the person had continued their Bronze membership, their total cost would have been:
70 + (3 x 40) = £190
Savings = £190 – £120 = £70
Hence, C is correct.