what do i need to do ?

Answer:
21
Step-by-step explanation:
This is an easy proportion. Let's say that x is the number of passes. We get:
[tex]\frac{7}{8} = \frac{x}{24}[/tex]
Now, solve for x by cross multiplying:
[tex]24(7) = 8x[/tex]
[tex]x = \frac{24(7)}{8} = 21[/tex]