To represent the ages of Lyle, Katrina, and Mari with \( x \) being Lyle's age, we can define their ages as follows:
- Lyle's age: \( x \)
- Katrina's age: \( x + 2 \) (the next even number)
- Mari's age: \( x + 4 \) (the following even number after Katrina)
Since their combined age is 66 years, we can write the equation as:
\[ x + (x + 2) + (x + 4) = 66 \]
Now, we can simplify the equation:
\[ x + x + 2 + x + 4 = 66 \]
Combining like terms gives us:
\[ 3x + 6 = 66 \]
Therefore, the equation that can be used to determine the age, \( x \), of Lyle is:
\[ ( x ) + ( x + 2 ) + ( x + 4 ) = ( 66 ) \]