these are all problems designed to practice the law of sine :
a/sin(A) = b/sin(B) = c/sin(C)
with a, b, c being the sides, and A, B, C being the corresponding opposite angles.
I
and remember :
sin(90) = 1
a)
4/sin(30) = c/sin(90) = c
4/0.5 = c = 8 cm
b)
17/sin(53) = c/sin(90) = c
c = 21.28630619... cm
c)
6/sin(41) = c/sin(90) = c
c = 9.14551852... cm