+50 f+s= total # of trips
x+y= amount of cement they bring when they each go one trip
xf + sy = total number of concrete they bring after all their trips
+1904 \(x\) = cubic yards of cement the first truck can hold at one time
\(y\) = cubic yards of cement the second truck can hold at one time
\(f\) = number of trips of the first truck
\(s\) = number of trips of the second truck
\(f+s\) = the combined number of trips between the first and second trucks
\(x+y\) = the combined cubic yards of cement that can be held between the first and second trucks
\(xf+sy\) = the combined cubic yards of cement delivered between the first and second trucks
