Amount of room hannah can paint in an hour = 1/20
amount of room destiny can paint in an hour = 1/16
number of hours = x
1/20x + 1/16x = 1
the reason why this formula is true is, the amount of the room painted in the end should be 1 (the whole room)
4/80x + 5/80x = 1
9/80x = 1
9x = 80
x = 80/9 hours
x = 8.89 hours
We need to solve the speed formula for d. To do so, let's start by moving the number of the left hand side:

Square both sides to get rid of the square root:

Now plug the known value of the speed to find the distance:

So the closest answer is the last one: d=0.155km
8
Reduce the expression, if possibel, by cancelling the common factors