I’m very confused, my teacher did not explain well.

In order for two triangles to be considered as similar, they must be
- equiangular (all angles equal)
- all sides equal (sss)
- if two pairs of two sides are in proportion or are matching, and one included angle is equal

Q4a) yes, because all the angles are equal (equiangular)

b) yes, because all sides are in matching ratio (so 10/5 is 2, 6/3 is 2 and 8/4 is 2; so they are in matching ratios)

c) yes, because if you plus 60 and 70, you get 130. Minus 180 and 130, you get 50. So, in both triangles the angles will be 60,70 and 50; so they're equiangular