Hi!
I would follow this reasoning:
- an increase of 15k in capacity (from 15k to 30k, which is the double) leads to an increase of 1.8M in costs (from 4.5M to 6.3M). An increase of only 9k (from 15k to 24k) how much would increase the costs?
- you can set up the following proportion, where x is the unknown variable representing the cost increase:
15k : 1,8M = 9k : x
x = (1.8M*9k)/15k = 1.08M
- in sum, bringing the capacity up to 24k (+9k from 15k) would bring the costs up by 1.08M, with new costs totaling 4.5M + 1.08M = 5.56M, which can be approximated with 5.6M
Hope this helps!