Solving equations, a couple questions!

I have these questions on my homework but I have no idea how the answer is how it is. Thank you for answering!

1. Solve this equation for C.

S=C+rC

*I know that the answer is S/1+r= c*

I do not know where the 1 comes from.

2. You have 36.75$ to spend on a sweathshirt. There is a 5% sales tax. What is the most the sweatshirt can cost?

*How do you solve this? *

3. Solve this equation for B1:

A=1/2h (b1 + b2)

*The answer is 2a/h -b1 *

Whenever I do it, I get 2a-b1/h

I do not know what I am doing wrong.

4. A garden is 46 feet wide and 84 feet long. The garden has a path around it that is 10 feet wide. The cost of fencing is 9$ per foot. How much will it cost to put a fence around the path?

Here, I do not get how to draw a picture or get the equation.

Thank you so much to anyone who takes the time to answer all of my questions! I have a midyear on monday and I really need to know these answers for it.