Question 550932
We know the total seats which are made up of main and back seats equals 20,000:
m+b=20,000

We know the earnings were 55 for every main and 45 for every back:
55*m+45*b=955,000

We now have a system of equations to solve. Lets multiply both sides of the first equation by 45


Now subtract :
45m+45b=900,000 from 
55*m+45*b=955,000

That gives us 
10m=55,000
so
m=5,500
And if we sub m back into our first equation we find that
b=14,500