Hi,
Let x represent Frank's mph. then Marcie's would be (x+1)mph
d = rt
write as we read***
6 = xt Or t = 6/x
8 = (x+1)t 0r t = 8/(x+1)
6/x = 8/(x+1)
cross multiply to solve
8x = 6(x+1)
8x = 6x + 6
2x = 6
x = 3mpr
Franks walks 3mpr and Marcie walks 4mph
checking our answer
6mi/3mph = 8mi/4mph