Equation for this problem: Total 3 cubed / (L x W)
So 18.5cm x 15cm = 277.5 is the product of L and W. Now you need to devide the total by 277.5 which is 14. So the aquarium is 14 cm deep.
To find the answer, we will need to divide 3/5 by 2/3.
3/5 / 2/3
3/5 x 3/2
9 / 10
There are 9/10 groups of 2/3 in 3/5.
Hope this helps!! :)
Choice C, because

So it's less than what she originally had (which isn't possible)
This is how I would solve it, I would act as if there were 36 people in the class.
36÷6=6×5=30
30÷3=10×2=20
20/36=10/18=5/9
You could also try another number such as 24;
24×(5÷6)=20
20×(2/3)=13.3(3 repeating)
13.333/24=5/9
5/9 people have dogs.
Tell me if this helps.