well, we know is not the picture of a cat, so those slanted lines are not whiskers, just tickmarks saying that those two sides are twins.
if the vertex above is 30°, the twin sides on this isosceles triangle will make also twin angles at the base, so 180° - 30° = 150°, so the twin angles share evenly those 150°, so each is 150°/2 = 75° = x.
