1. The problem statement, all variables and given/known data Now, suppose the student wishes to bring back some ice cream from the restaurant for her friends at school, but since it is such a hot day, the ice cream will melt away in the car in only 5 minutes. How fast will the student have to drive back to get the ice cream to her friends before it completely melts? Knowns: C=40mph(for these problems) Time=5 minutes Distance=7.5 miles 2. Relevant equations Dt= change in time p= proper interval Dt-p= d/v Dt-p=Dt/lambda or dt/sqrt(1-v^2/c^2) 3. The attempt at a solution Dt-p=7.5m/40mph=.1875hr .1875=(5minutes/60minutes per hour)/sqrt(1-v^2/40^2) rearranging it becomes: v=sqrt( -((.083hr/.1875hr)^2-1)*40^2) answer I get is 35.8mph The online homework tells me I am wrong either by sig figs or by bad rounding.