Answer:
x = 27
Explanation:
I'm going to use letters to label the parts of the triangle while explaining how to solve for x:
Angle A = x (bottom left angle of the triangle)
Angle B = 4x (top angle of the triangle)
Angle C = empty angle (bottom right angle of the triangle)
Angle D = 3x + 54 (angle outside of the triangle)
A line has a angle measurement of 180 degrees.
Angle C & D make up the line, meaning Angle C + Angle D = 180 degrees.
To find Angle C, we would subtract Angle D's equation from 180 like this:
180 - (3x + 54)
Now Angle C equals 180 - (3x + 54)
Now we have all the angles inside the triangle. To find x, we are going to sum up Angle A, B, & C and set it equal to 180.
We set the equation to 180 because a the sum of the interior angles for a triangle is 180.
The equation looks like this:
(180 - (3x + 54)) + 4x + x = 180
Now we use basic algebra to solve it:
(180 - (3x + 54)) + 4x + x = 180
(distribute the - to (3x + 54))
180 - 3x - 54 + 4x + x = 180
(add like terms on the left side of the equation)
126 + 2x = 180
(subtract 126 from both sides)
2x = 54
(divide both sides by 2)
x = 27
To prove this answer is correct, plug it back in the original equation and you'll see that it ends up equaling 180, which is the sum of interior angles for triangle.
Hope it helps (●'◡'●)