The total amount that all the angles inside the triangle equal is 180°.
So you can write an equation with the given
3x+5 + 2x+18 + 2x+17 = 180
Combine all like terms
7x + 40 = 180
subtract 40 from both sides
7x = 140
divide both sides by 7
x = 20
Then you plug that into the angles and find out how much each is
3x + 5
3(20) + 5
60 + 5
65
2x + 18
2(20) + 18
40 + 18
58
2x + 17
2(20) + 17
40 + 17
57
Hope this helps :)