Assuming this question is about total costs in an economics term then this is fixed costs + variable costs in whichever currency is being talked about..
Let’s make an equation Let’s say x = amount of years after Smith = 8, mother = 42 3(8 + x) = 42 + x 24 + 3x = 42 + x 2x = 18, x = 9 Solution: after 9 years
