As per the problem
Erika drove 280 miles in 5.5 hours.
She averaged 40 miles per hour driving through towns and cities .
She averaged 55 miles per hour driving on the highway.
Let Erika drive on high for "t" hours on highway.
Then driving time other than highway[tex] =(5.5-t) \ hours\\ [/tex]
As we know that [tex] \text{Distance=Speed*Time}\\ \\\text{Hence from the given data we can setup the equation as below}\\\\ [/tex]
[tex] 40(5.5-t)+55(t)=280\\\\\text{Simplify we get}\\\\ 220-40t+55t=280\\\\\text{Take the like terms together and simplify we get}\\\\55t-40t=280-220\\\\15t=60\\\\t=4\\ [/tex]
Hence for 4 hours Erika drove on the highway.
