Assuming that you mean to put n instead of 5, this is demonstrating The Identity Property.
The identity property is the property that states that by adding 0 to a number, you don't change the value. For example, 510 + 0 = 510.
Answer:
The answer to your question is x = 4d/t - S1
Step-by-step explanation:
Data
total time = t = 2.75 hours
Initial speed = S1 = 55 mi/h
Final speed = x
distance = d = 60 mi
Formula
speed = distance / time
Average speed = (Initial speed + final speed)/2 or
= (S1 + x)/2
Substitution
(S1 + x)/2 = 2(d) / t
Solve for x
x = (2d/t)2 - S1
Simplification and result
x = 4d/t - S1