a triangle equals 180 drgrees. since it's a ratio, 8, 7, & 5 times a number (x) equal to 180. this can be represented by the equation:
8x+7x+5x=180
you have to solve for x of course but you aren't done yet. Which part of the ratio(8 : 7 : 5) represents the smallest angle? (hint: it's the smallest number.)
now that you've found x (measurement if the ratio was 1 to something, instead of 8, 7, and 5, and etc.) and the number for the smallest angle in the ratio, multiply them to get the measurement of the smallest angle.
I hope this makes since. Good Luck!