let

x = the measure of the first angle

y = the measure of the second angle

z = the measure of the third angle

the measure of the second angle is 2 times the measure of the first angle

y = 2x

the measure of the third is 40 degrees more than the first angle:

z = 40 + x

since we are talking about angles in a trangle we have:

x + y + z = 180

by solving the system of equations:

y = 2x

z = 40 + x

x + y + z = 180

we find:

x = 35 degrees

y = 70 degrees

z = 75 degrees

click here to see the step by step solution of the system of equations:

the measure of the thrid angle is 75 degrees.