Given the cost of $28 to rent a trailer for an x amount of hours:
The expression is 28x
Answer: 
Step-by-step explanation:
For this exercise it is important to remember the following:

Given the following expression:

You can notice that the radicand (the number inside the square root) is negative. Therefore, in order to simplify the expression, you need to follow these steps:
1. Replace
with
and simplify:

2. Descompose 12 into its prime factors:

3. Substitute into the expression:

4. Since
, you can simplify it:

I don't know what the "lowest y-intercept means" so if you can reiterate and clarify I'd appreciate it, but if you understand what you're looking for then I assume that a graph would be helpful. An online useful graphing site I like is desmos. Hope I helped.