we write teo equations for each statement
an evening flight had six less than twice the number of passengers that a morning flight

the total number of passengers on both sides was 753

where e is the passengers on evening flight and m the passengers on morning flight
we will solve two equations with two unknowns

we will use the substitution method
we wiil replace the value of e from the first equation on the second

now solve for m

the morning flight had 253 passengers