To find the value of x in the first equation:

1) 5/12 = 25/x

Cross multiply:
5x = 12 * 25
5x = 300

Divide both sides by 5:
x = 300/5
x = 60

Therefore, x = 60 in the first equation.

To find the value of x in the second equation:

2) 3/x = 75/100

Cross multiply:
3 100 = 75 x
300 = 75x

Divide both sides by 75:
x = 300/75
x = 4

Therefore, x = 4 in the second equation.