When adding or subtracting fractions, multiply to get the same denominator (bottom number).

When multipling two fractions, just multiply straight across, factor diagonally if possible.

When dividing fractions, flip the second fraction over and multiply.

For the polynomials, you just need to combine like terms.
3x + 4y² + 7x + 6y² = (3x + 7x) + (4y² + 6y²) = 10x + 10y²
You can factor this further but I don't know if its necessary.
= 10(x + y)
Let me know if you have any questions.