They are parallel because they have the same slope
0.5 x 4 = 2 feet / 2 feet in 4 seconds
15 - 2 = 13
New depth: 13 feet
0.4 x 3 = 1.2 feet / 1.2 feet in 3 seconds
13 - 1.2 = 11.8
New depth: 11.8 feet
I do not think we need to rewrite the first two numbers in the given above because they are already the simplest forms of themselves being whole numbers. However, the third number may be rewritten as 1/2 by dividing both numerator and denominator by 5 and the last one as 2/25 by dividing both numerator and denominator by 4.
