x = 31
since the two angles added together would make 180°, the equation should look like this:
x + 87 + 2x = 180
Combine like terms (aka just add the two variables together)
x is equivalent to one, so 1x + 2x = 3x.
3x + 87 = 180
Subtract by 87 on both sides.
3x + 87 - 87 = 180 - 87
87-87=0, 180- 87 = 93, so this leaves the equation like this
3x = 93
Now divide by 3 on both sides.
3x / 3 = 93 / 3
3/3 = 1x, which can just be written as x, and 93/3 = 31
x = 31
You can check if this is correct by replacing x with 31, then adding the two angles together to see if they equal 180°.
31 + 87 = 118
2 * 31 = 62
118 + 62 = 180°