The expression $4y^2 - 3y^2$ can be simplified by combining like terms.

$4y^2 - 3y^2 = (4 - 3)y^2 = 1y^2 = y^2$

So, the simplified expression is $y^2$.

Would you like more details or have any questions?

Here are some related questions you might find helpful:

1. How do you simplify expressions with multiple variables?
2. What is the difference between like and unlike terms?
3. How do you factor quadratic expressions?
4. Can you explain the distributive property in algebra?
5. How do you solve equations involving exponents?

Tip: When simplifying algebraic expressions, always look for like terms to combine.