asap i need help quickly

Answer:
x = 15
Step-by-step explanation:
Angles in a triangle add up to equal 180
Hence, 3x + 5x + 4x = 180
( Note that we've just created an equation that we can use to solve for x)
We now solve for x using the equation created
3x + 5x + 4x = 180
Combine like terms
12x = 180
Divide both sides by 12
x = 15
Answer:
x = 15
Step-by-step explanation:
The sum of the angles of a triangle is 180
3x+4x+5x = 180
Combine like terms
12x = 180
Divide by 12
12x/12 =180/12
x = 15