We have the expression:

When we have rational functions, where the denominator is a function of x, we have a restriction for the domain for any value of x that makes the denominator equal to 0.
That is because if the denominator is 0, then we have a function f(x) that is a division by zero and is undefined.
If we have a value that makes f(x) to be undefined, then this value of x does not belong to the domain of f(x).
Expression:

Answer: There is no restriction for x in the expression.
Solve;
If each cm = 4 meters, then you multiply.
4*2
= 8
There are 2 cm, each cm = 4 meters, so you multiply to get your answer.
The final height of the door is 8 meters.
Answer: 7
Work: So, the goal is to get z alone, so we are going to add 85 on both sides, cancelling on the side it's currently on. So, the new equation is going to be 25z = 175. Then, to get z even more lonely, we are going to divide 25 on both sides, and again cancelling it on the side it's currently on. So, the answer is z = 7. I hope this helps, and Happy Holidays! :)
X+10=105
105-10=95=x
x = 95