To solve this proportion, first convert the mixed numbers to improper fractions:

7 1/2 = 15/2
4 1/2 = 9/2

Now the proportion becomes:

15/2 : 9/2 = x : 3/25

Cross multiply to solve for x:

(15/2) (3/25) = (9/2) x
(45/50) = 9/2 * x

Simplify:

9/10 = 9/2 * x
9/10 = 9x/2

Now, isolate x by multiplying both sides by 2/9:

(2/9) (9/10) = (2/9) (9x/2)
2/10 = x
1/5 = x

Therefore, x = 1/5.