I need to figure out how exactly to solve this and find the answer to x

Since a triangle has 180 interior degrees, and 81+57=138, and 180-138=42, you need to find _*2+18=42. (Hint, you can subtract the 18 from the 42, and find _*2=24).

Step-by-step explanation:

yes because there is exactly one y value for every x value

for function there can't be more than one value for every x value