Question 1165874
{{{x}}} = miles driven into the country = miles driven in the return trip
{{{x/40}}} = hours driving into the country
{{{x/30}}} = hours spent driving back from the country to the man's home
{{{1}}} hours spent not driving, included in the {{{8-hour}}} trip
{{{x/40+x/30+1=8}}}
Multiplying each side of the equal sign times {{{120}}} , we get
{{{120(x/40+x/30+1)=120*8}}}
{{{120(x/40)+120(x/30)+120*1=960}}}
{{{3x+4x+120=960}}}
{{{7x+120=960}}}
{{{7x+120-120=960-120}}}
{{{7x=840}}}
{{{x=840/7}}}
{{{highlight(x=120)}}}