Greetings Alice!
The objective here is to calculate what value of x for which that statement is true. X itself is just a variable which cab take on any value we need it to but may not necessarily result in the right answer. Case in point, let's pick a value at random: 20.
If X were 20 then the equation would look like this:
20/5 = 70
As we know though, 20/5 is 4, which is NOT 70. Therefore, the question we are asking ourselves is "what is the value of a number that equals 70 when it is divided by 5?"
Since we are talking about Algebra here, we can actually reask the question in a slightly different way. See, when you have an equation you can do whatever mathematical operation you want to one side provided you do the exact same thing to the other side. In this example we can multiply both sides by 5 and simplify both sides to get this:
5 * (x/5) = 70 * 5
See now that on the left side. of the equation, you are simply left with x? This is because we are both multiplying and dividing x by the same number, which has the net effect of multiplying x by 1. The right side of the equation becomes 70 * 5, which equals 350.
So you see, we've changed our question to "what number is 70 times 5?" The answer is x = 350!
What it boils down to is that sometimes in algebra you are given the answer first, and must then seek to ask the right question.
Have a good day!
1/30/2013

Tristan N.