let's recall that a triangle has a total of 180° for its interior angles.
x = first angle
3x = second angle, three times the first one
5x = third angle, five times the first one, and largest.
[tex]\bf x+3x+5x=180\implies 9x=180\implies x = \cfrac{180}{9}\implies x = 20 \\\\\\ \stackrel{largest}{5(x)}\implies 5(20)\implies 100[/tex]