Answer:
x=3.5
Step-by-step explanation:
We can use proportions to solve this problem. Put the side of one triangle over the same side of the other triangle.
6 4.2
------ = ----------
5 x
Using cross products
6x = 5*4.2
6x =21
Divide by 6
6x/6 = 21/6
x=3.5
Step-by-step explanation:

Or basically,

or

You can’t really find the sum unless there is number to plug in for the variables.
Answer:
I feel like I should know this cause I'm in year 8
Step-by-step explanation:
Yet I have no clue what any of that is, I need to listen in class