Which equation shows the substitution method being used to solve the system of linear equations?

x – y = 7
x = y + 3

a.
(y + 3) – y = 7

b.
x = (7 – x) + 3

c.
x – (y + 3) = 7

d.
x – y = y + 3

Dylan and dusty plan to take weekly surfing lessons together. if the 2-hour lessons are $20 per person and they plan to spend $100 each on new surfboards, what is the maximum number of lessons the two can take if the total amount spent for lessons and surfboards is at most $480?

Diana is painting statues she has 7/8 of a liter of paint each statue requires 1/20 of a liter of paint how many statues can she paint?

Angles r and s are complementary. the measure of angle r is 31 degrees. which equation can be used to find angle s?