The top row contains the product of

with each term of the expressions

and bottom row contains the product of -1 with each term of expression

.
The final result will be the sum of terms of both rows as shown below:
So the correct answer is option D
The time it took to complete 12 laps.
The independent, however, would be the car's speed or something like that.
Boys:girls = 4/5
boys = 4/(4+5) = 4/9 of the class