Let the numbers be a and b and let b be the second number, so b=3a-9.6 and a+b=7.2, and b=7.2-a. Substitute this in the other equation: 7.2-a=3a-9.6; 4a=7.2+9.6=16.8, so a=16.8/4=4.2. Therefore b=7.2-4.2=3. Check these values for a and b: b=3a-9.6: 3=3*4.2-9.6=12.6-9.6=3. Correct!