Hi! I'm happy to help!
To first solve this, Let's see if we can simplify our expressions using the order of operations: our original expression cannot be simplified. The first expression cannot be simplified. The second expression we can multiply the outside by the parenthesis by the inside, same with the third and fourth.
(make sure everything outside of the parenthesis is being multiplied by each part inside of the parenthesis)
9a²b²
9a²b²
3ab(3b+2a)
ab(9b+6a)
b(9ab+6a²)
9ab²+6a²b
3ab(2b+3a)
ab(6b+9a)
b(6ab+9a²)
6ab²+9a²b
3a²b²(2b+3a)
a²b²(6b+9a)
b²(6a²b+9a³)
6a²b³+9a³b²
Now that we have all expressions fully simplified, let's compare to see which one matches.
Our first expression is nowhere close to what our original expression is, 1 is incorrect.
Our second expression is close, but it has the 9 and the 6 flipped, even if we rearrange the expression like this, 6a²b+9ab², it still doesn't match, so 2 is also incorrect.
Our third expression has the correct numbers, variables, placement, and exponents, so 3 is correct.
Our fourth expression has incorrect exponents, the expression made every variable multiplied by ab an extra time, so 4 is incorrect.
In summary, you should pick number 3, because it is equivalent.
I hope this was helpful, keep learning! :D