How many vehicles carry 3 crew members?

Question

There are 24 space patrol vehicles in a hanger. Some of the vehicles carry 3 crew members. The others carry 4 crew members. All 86 crew members are at a briefing. How many vehicles carry 3 crew members?

Answer 1

10 vehicles carrying 3 crew members

Answer 2

x+y=24 where x=# of vehicles carrying 3 people and y=# of vehicles carrying 4 people

3x+4y=86

x+y=24 means x=24-y

substitute

3(24-y)+4y=86

72-3y+4y=86

72+y=86

y=86-72

y=14 vehicles carry 4 members

24-14=10 vehicles carry 3 members