Replace the x with a number so that 5/12 = x/48.

20

Explanation: When we have two fractions alike we can cross multiply to find the value of x. So, that means 12x=48*5

Simplify to get: 12x=240

x=20

x = 20

Explanation:

5   =    x                                  

12      48         12 x 4 = 48

                      5 x 4 = 20                 x = 20

Multiply both sides by 4 because whatever you do to the bottom half, you do to the top

Hope this helps :)