Question

On one flight, the airline sold twice as many economy class tickets as business class tickets. Economy class costs $400 and business class costs $900. Five of the economy class ticket holders redeemed a voucher and did not have to pay. The total revenue of the flight was $49 000.
a) Solve the equation 900n+400(2n-5)=49000 for n, the number of business class travellers
b) How many travelled economy class?