You multiply both of the equations until you have two of the same term the same like for example, say I have 4x and 5x. You want to multiply until both have the same number, so multiply 5x by four, then multiply 4x by five, and you will get 20x, then both of those cancel out and you will be left with the other variable, and you just solve like a normal equation.
This is a pythagorean triple --> 3-4-5
Although you notice it is doubled but with the same pattern --> 6-8-10
Thus, the hypotenuse is 10.
The answer is A- between 8 m& 12m
