10th grade math hw! - Please don't answer unless you're gonna explain how you got it . I have the answer ( my teacher posted an answer key ) i just need to understand

Solve the given system of equations. 2y= -x+9 , 3x-6= -15

Astudent is determining the influence of different types of food on the growth rate of spiders. she feeds one group of spiders two caterpillars twice a week. the other group received similarly-sized beetles twice a week. she records the amount of time required for individuals to reach sexual maturity. her hypothesis is that the spiders feeding on caterpillars will have a faster growth rate because caterpillars have a higher protein content compared to beetles. in this experiment, what is the dependent variable? spiders assigned to different feeding groups. time required to reach sexual maturity number of prey items fed twice a week. growth rates of each group.

Suppose you can spend at most $12. create an inequality that represents this restraint. then find at least three ordered pair solutions representing the number of boxes of candy and combos you can buy