Hi everybody

I know already the solutions for these questions. But i can't find the way how to get it.

1. question: A boutique owner starts her business with a debt of $100000. At the end of the 5th year, she has made a profit of $40000. Assuming that her profits rose linearly through the years, what was the rate of increase of her profit per year?

solution: $28000

I have no idea how to begin this problem..

2. question: In the general form, the supply and demand functions are written as p-0.25q-8=0 and p+0.7q-12=0 respectively. p is given in $. Find and interpret the market equilibrium point.

solution: $9

0.25q + 8 = -0.7+12 --> an then I get 0.2375. I don't know how my teacher get to $9.

Thank you very much for any advice and help.