Solve the proportion

5/x = 4/8

A. 2

B. 6

C. 8

D. 10

Cross-multiply for a result of:

40=4x

Divide by 4 to see that x=10. D is the correct answer.

5/x = 4/8

Simplify the fraction 4/8

Divide both the numerator and denominator by 4 to get 1/2

5/x = 1/2

Now, we cross multiply: a/b = c/d ⇒ ad = bc

5/x = 1/2

1 (x) = 5 (2)

x = 10

Your final answer is D. 10.