To solve this equation, we first need to simplify the left side by multiplying the fractions:

(-5/14) * (21/25) - y = 3.3/4

(-105/350) - y = 3.3/4

Next, we need to convert the mixed fraction 3.3/4 into a fraction:

3.3/4 = 3 + 3/10 = 30/10 + 3/10 = 33/10

Now, the equation becomes:

(-105/350) - y = 33/10

To simplify further, we need to find a common denominator for y:

(-105/350) - y = 33/10

(-105/350) - (350y/350) = 33/10

Now, we can combine the terms on the left side:

(-105 - 350y)/350 = 33/10

To clear the fraction, we can multiply both sides by 350:

-105 - 350y = 33(35)

-105 - 350y = 1155

Add 105 to both sides:

-350y = 1260

Now, divide by -350 to solve for y:

y = -1260/350 = -126/35

Therefore, y = -126/35.