How do u do this? ! show me how
part a and b especially b!

Check the picture below.

in the picture below, the bottom part

notice, 69° + 21° = 90°, so 21° and 69° are really complementary angles, sharing the same quadrant, meaning for any two sides of lengths say, a,b one angle will have a tangent of say b/a, then the other will have a tangent of a/b.

namely the tangent of each angle, is simply the other's tangent upside-down.

(sin 42)/31. = sinx)/37

sinx = 37 (sin42)/31

= 37× 0.66/31 = 0.787

x= 51.9

other angle opposite to y = 180-51.9-42

= 180- 93.9 =86.1

so

sin42)/31 = sin 86.1)/y

0.021 = 0.997 /y

y= 0.997/0.021 =47.47