Find the length of this right triangle. give an approximation to 3 decimal places

A triangle always has 180 degrees so to find the missing number do:

21+17+a = 180

38+a=180

180-38=a

a= 42

the answer is 42

it's d.

step-by-step explanation:

because: -1(4x + 1y) +2 (1x-3y) distribute each number into the parenthesis.

then you would get: -4x - 1y + 2x -6y combine like terms

and get: 2x -7y

hope my answer has you if not then i'm sorry.