Let George's age be x. Then Alex's age is x+12 and Carl's is 3(x+12). Their ages add up to 68 so we can form an equation.
x+(x+12)+3(x+12)=68
2x+12+3x+36=68
5x+48=68
5x=20
x=4
So George's age is 4, Alex's is 16, and Carl's is 48. The ratio of their ages is:
4:48:16
=1:12:4