I need to find the equation as well as the age.

Xavier and Yifei have been married for exactly 35 years. Yifei is eight years older than Xavier. Now the sum of their ages is 124. How old was Yifei when they were married? a. Set up and write an equation that represents the unknown ages in terms of Yifei's age when they were married. (The variable should represent Yifei's age when they were married.) b. Determine how old Yifei was when Yifei and Xavier were married