Solution:
Bobby age: 61 years.
Analysis:
We have two variables, and we will assign as X and Y:
X: Bobby age
Y: Kayla age
According to the problem, we can write two linear equations:
Bobby is 12 years older than Kayla: X=Y+12
The sum of their ages is 110: X+Y=110
In this case, we can replace value of X in the second equation and isolate Y:
X+Y=110
(Y+12)+Y=110
2Y+12=110
2Y=110-12
2Y=98
Y=98/2
Y=49
As we know the value of Y, now we find value of X
X+Y=110
X+49=110
X=110-49
X=61.