We call "y" total renting costs and "x" total vacation days
according to that in first case we have:
y = 100*x + 50
And for the second case
y = 120*x + 10 (1)
That two equation system represent the equation system of the situation, therefore if we solve that system we will determine the choises with same costs
equating these two equations:
100*x + 50 = 120*x + 10
50 - 10 = 120*x - 100*x
20*x = 40
x = 2 days
Plugging that value in any of the equation (1) or (2) we get y value
