The proportion would be 34/75 = y/100 because if 34 is 75%, y is 100%.
To solve you could either use cross products or basic multiplication.
To use cross products, multiply diagonal numbers.
34 × 100 = 3400
75 × y = 75y.
To solve, you divide each side by 75.
3400 ÷ 75 = 45 1/3
75 ÷ 75 = 1
y = 45 1/3
The other method for this would be to use multiplication. Seeing that 75 is 3/4 of 100, you would multiply 34 by 3/4, giving you 45 1/3. Hope this helps! :D