To simplify the equation, we can start by simplifying the right side of the equation:

5² = 25 (5/4)² = (5/4) * (5/4) = 25/16

Now, we can substitute these values back into the equation:

y² = 25 - 25/16

To combine the fractions, we need a common denominator:

y² = (25 * 16/16) - (25/16)

y² = (400/16) - (25/16)

Now, we can subtract the fractions:

y² = (400 - 25)/16

y² = 375/16

Therefore, the simplified equation is y² = 375/16.