7v + 12b = 640
12v + 6b = 456
Multiply the bottom equation by -2 in order to cancel out 12b with 6b.
7v + 12b = 640
- 24v -12b = -912
-17v = -272
17v = 272
v = 272/17
v = 16 students
If we use this: 7v + 12b = 640 ;then:
7(16) +12b = 640
112 +12b = 640
12b = 640 -112
12b = 528
b = 528/12
b = 44 students
So the number of students in each van is 16, and number of students in each bus is 44.