Answer: 75.143 mph
Step-by-step explanation:
First you need to set up the equation
252=14(s-60)+40
Get rid of the parenthesis by distributing the 14
252=14s-840+40
combine like terms
252=14s-800
rearrange so the variable is on the left then combine like terms again.
-14s= -252-800
-14s= -1052
divide both sides by -14
s= 75.143