So first you want to draw out you triangle and label everything so side a would be x, side b would be 15 and c would be x
next the angles need to be label
and finally the anwser is 150m
Get a math app, and get the answers from it. some will show you step by step
Answer:

Step-by-step explanation:
Let here the given function f(x) = y
or, 
⇒ y = 3x+ 9
Now, solving for x, we get
3x+ 9 = y ⇒ 3x = y - 9
or, 
⇒ 
Now, substituting x and y
Hence, 
Answer:
a = 20
Step-by-step explanation:
The mean is calculated as
mean = 
=
= 
Then
= 27 ( multiply both sides by 5 to clear the fraction )
115 + a = 135 ( subtract 115 from both sides )
a = 20