When you have a variable in an equation, you have to isolate it on one side. To do this, look for any other numbers and if they are added, multiplied, divided, or subtracted from x.
Next, you take that number and do the opposite of its operation to the other side.
In this example, you have x/5=20
So we first identify that x is being divided by 5
Then we take 5, and do the opposite of division to 20.
So x/5=20 turns into x = 5x20
Then we simplify, x = 100.
If your not sure your answer is write, you can always put the value of x back into the first equation and solve to see if its true:
X/5=20
100/5=20
20=20