For this case we have to:
x: Variable that represents Tyler's age
y: Variable that represents Tiffany's age
According to the data of the statement we can propose the following equations:

To solve we substitute the first equation in the second equation:

So, Tiffany is 14 years old.
Then Tyler has:

Tyler is 18 years old.
Answer:
Tyler: 18 years old
Tiffany: 14 years old