Let beA
Let beB
Let beC



1st method
3B = 60
so B = 20
2A+B= 28
2A=28-B=4
so A=2
2A+C=10
C=10-2A=2
so C=2

2nd method
3B=60
B=60/3
   =20
So A=20
2A+B=28
2A+20=28
28-20=2A
8=2A
A=8/2
   =4
So A=4
2A+C=10
2(4)+C=10
10-8=C
2=C
So C=2