Question 741976
Let A =  Alice's age and D = Dan's age
Then, A + D = 110 and D = A + 2

Using the substitution method, we will substitute the equation D=A+2 into the first equation to get:

A + A + 2 = 110
2A + 2 = 110  Collect like terms
2A = 108  move the 2 to the other side of the equation
A = 54, which is Alice's age

D = A + 2 so D = 54 + 2 = 56, which is Dan's age