See description in the pic.
Answer:

Step-by-step explanation:
We will use the co-function identity for sine, where:

Since sin(21)=0.358=cos(x). This means that:

Solve for x. Add x to both sides:

Subtract 21 from both sides:

Hence:

21/1 divided by 7/4 = 21/1 x 4/7 = 12.
Hope this helped my guy.