Yes- though we may say "When will we ever use this?" ever so often in class, the reality is that we use mathematics in everyday life. From simple addition, to factoring, to finding the angles of various components to a building, math is always being used in real life.
Question 5, x could be either 6 or -1.
I assume you are asking one of three things, so I will answer all of them.
if you are asking what is 1/2 of 312, then multiply 312 by 1/2. 312 is really just 312/1, so

we multiply fractions by multiplying straight across

if you were asking what part of 3 1/2 is 1/2 then we have to recognize what 3 1/2 is as an improper fraction. to do this, we convert 3 into halves. how many halves of pizza are there in 3 whole pizzas? 6. so we have 6 halves and one half, which is a total of 7 halves.

now, we do the same thing as the first problem

if you were asking what is half of 3.12, then we convert 1/2 to a decimal and multiply