Question 4474
Let the first angle = x
let the second angle =2x
let the third angle = 2x-20

the total measure of the angles of a triangle is 180 degrees:
180=x+2x+(2x-20)
180=5x-20
200=5x
x=40

so the first angle measures 40 degrees
the second is twice that, or 80 degrees
and the third is the second angle minus 20, or 60 degrees.