Let's go through each of the problems in the image, simplifying by collecting like terms:

a) $2x + 5x - 4x$

Combine the terms with $x$: $(2x + 5x - 4x) = 3x$ So, the simplified result is $3x$.

b) $7y + 5 - y$

Group the like terms, where $7y - y$ gives: $(7y - y) + 5 = 6y + 5$ So, the simplified result is $6y + 5$.

c) $4x - (-4x)$

When subtracting a negative, it becomes addition: $4x + 4x = 8x$ So, the simplified result is $8x$.

d) $3x + 12y - 3x + 5y$

Group the like terms: $(3x - 3x) + (12y + 5y) = 0 + 17y$ So, the simplified result is $17y$.

e) $3a + 4a^2 + 7a + 5a^2$

Group the like terms: $3a + 7a + 4a^2 + 5a^2 = 10a + 9a^2$ So, the simplified result is $10a + 9a^2$.

f) $3xy - 4xy + 2yx - 3y$

First, recognize that $xy$ and $yx$ are the same. Group the like terms: $(3xy - 4xy + 2xy) - 3y = 1xy - 3y = xy - 3y$ So, the simplified result is $xy - 3y$.

Would you like further explanations or assistance with any specific part? Let me know if you have any questions or need more practice problems!

Here are five related questions for further practice:

1. Simplify: $6a + 3a - 4a$
2. Simplify: $5x^2 + 3x - 2x^2 + 6x$
3. Simplify: $8m - 5n + 2m + 3n$
4. Simplify: $2b^2 - 3b + 4b^2 + b$
5. Simplify: $7x - 2y + 4x - y$

Tip: Always collect terms with the same variables or powers together to simplify efficiently!