Algebra question... where did 59.4 come from

Question

Sue has a 86 quiz average and a 93 for the lab grade. What does Sue need to get on the final to get a 90 for the course?

15% for the quiz average
50% for the lab grade
35% for the final exam

I have to set up an equation which was given to us as 59.4 + .35x = 90.

I know how to do the problem, but I can't figure out where 59.4 came from.

Answer 1

86(.15) + 93(.5) = 59.4