.
Dan drove to the lake and back. On the trip there he drove 30 mph and on the return trip he went 40 mph.
How long did the trip there take if the return trip took 3 hours
---------------------------------------------------------------
Your equation is
x*30 = 3*40.
The right side is the distance to the lake.
The left side is the distance back.
The equation says the distances are the same.
x is an unknown speed on the trip to the lake.
x = = 4 hours.
Answer. 4 hours.