Let f=first angle, s=second angle, t=third angle
the measure of the first angle is twice the measure of the second angle
he measure of the third angle is 20 degrees less than the second angle
The sum of all of the angles in a triangle equal 180 degrees
Plug in f=2s into f and plug in t=s-20 into t of
Notice how I substituted to have only one variable in the equation
solve for s
Add like terms
Plug s=50 into f=2s
Plug s=50 into t=s-20
So the 1st angle is 100 degrees, the 2nd angle is 50 degrees, and the 3rd angle is 30 degrees
Check:
Works