Since the triangle is equilateral (you can tell by the tick on each side), all angles have the same measure as well.
The angles of a triangle sum up to 180 degress, so three equal angles must measure 60 degrees each.
So, in particular, we have
[tex] 7x+4 = 60 \iff 7x = 56 \iff x=8[/tex]
x = 8 and y = 6
ΔRST is an equilateral triangle
with all 3 sides equal in length and all 3 angles = 60°, hence
7x + 4 = 60 ( subtract 4 from both sides )
7x = 56 ( divide both sides by 7 )
x = 8
similarly
8y + 12 = 60 ( subtract 12 from both sides )
8y = 48 ( divide both sides by 8 )
y = 6
