Label the slope and y intercept

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?

Icould really use some with this question.

45% of the trees in a park are apple trees. there are 27 apple trees in the park. how many trees are in the park in all?