p=2x+y, y=x+5, so x=y-5 making the first equation:
p=2(y-5)+y perform indicated multiplication on right side
p=2y-10+y combine like terms on right side
p=3y-10, and we are told that 71 passengers are transported so:
3y-10=71 add 10 to both sides
3y=81 divide both sides by 3
y=27
So the larger bus has 27 seats. (the smaller has 22 seats)