When using the substitution method for solving a system of linear equations in two variables, what should be the first step?

Adaylily farm sells a portion of their daylilies and allows a portion to grow and divide. the recursive formula an=1.5(an-1)-100 represents the number of daylilies, a, after n years. after the fifth year, the farmers estimate they have 2225 daylilies. how many daylilies were on the farm after the first year?

The angle of a triangle are given as 6x,(x-3), and (3x+7). find x then find the measures of the angles

Me with this one question, and i'll upvote the brainliest answer