a)

2/7 = 3/4x

To solve for x, we first need to cross multiply:

2 4 = 7 3

8 = 21

Therefore, the equation is not true and has no solution.

b)

21/25 = 49/50x

Cross multiplying:

21 50 = 25 49

1050 = 1225

Therefore, the equation is not true and has no solution.

c)

16/19 = 32/38x

Cross multiplying:

16 38 = 19 32

608 = 608

Therefore, the equation is true and x = 1.