To simplify the expression $7a(a - 3ab)$, we follow the distributive property, where we multiply $7a$ by each term inside the parentheses:

$7a(a - 3ab) = 7a \cdot a - 7a \cdot 3ab$

Now, simplify each term:

1. $7a \cdot a = 7a^2$
2. $7a \cdot 3ab = 21a^2b$

Thus, the simplified expression is:

$7a^2 - 21a^2b$

Would you like further details or have any questions?

Here are 5 related questions for further practice:

1. Simplify $5x(x - 2xy)$.
2. Expand and simplify $8m(m - 4mn)$.
3. Factor $9a^2 - 36ab$.
4. Expand and simplify $4x(2x + 3xy)$.
5. Simplify $6p(p - 5pq)$.

Tip: When using the distributive property, always ensure that you multiply each term in the parentheses by the outside term carefully.