Question 328458
D=RT
FOR THE FIRST PART OF THE TRIP;
76=RT
T=76/R
FOR THE SECOND PART OF THE TRIP:
2=(R-6)T
T=2/(R-6)
76/R+2/(R-6)=3
(76(R-6)+2R)/R(R-6)=3
(76R-456+2R)/(R^2-6R)=3 
(78R-456)/(R^2-6R)=3 CROSS MULTIPLY.
78R-456=3(R^2-6R)
78R-456=3R^2-18R
3R^2-18R-78R+456=0
3R^2-96R+456=0
3(R^2-32R+152)=0
{{{x = (-b +- sqrt( b^2-4*a*c ))/(2*a) }}}
R=(32+-SQRT(32^2-4*1*152])/2*1
R=(32+-SQRT[1,024-608])/2
R=(32+-SQRT416)/2
R=(32+-20.396)/2
R=(32+20.396)/2
R=52.396/2
R=26.198 MPH. ANS.
PROOF:
76/26.198+2/(26.198-6)=3
2.9+2/20.198=3
2.9+.1=3
3=3