Company A
Income = 35,000 + 0.03x
Company B
Income = 25,000 + 0.05x
set them equal to see how much of sales Julia needs to make the same income at both companies.
30,000 + 0.03x = 25,000 + 0.05x
30,000 - 25,000 = 0.05x - 0.03x
5,000 = 0.02x
5,000/0.02 = x
250,000 = x
Company A has better base salary and so would pay better if less than 250,000 sales are made. Company B has bigger percent bonus and would be a better deal if more than 250,000 sales are made.
So it's the 2nd choice.