(y-2)x i need like i don't understand me or i will fail math

OK, you need to distribute the x.  Think of it as spreading it out into the parentheses.

(y-2)x becomes xy-2x

Just to show you another one so you get the concept.

If you had 3(x+5+y) it becomes 3x+15+3y.  You spread the 3 out to multiply it by everything in the parentheses.

If that does not make sense feel free to ask me because this concept will come up again and again.

Hope that helps.

2.) is the most sense

Maybe the answer is 20mm. all i really did was just multiply, which is obvious.