Question 908864
Hey.I'm glad to help you.But my English isn't very well and I hope you don't mind it.

The answer is 55.

let William's age = x
let  Luis's age =x-30

 x-15 = 4·(x-30-15)
 x-15 = 4·(x-45)
 x-15 = 4x-45×4
 x-15 = 4x-180
 4x-x = 180-15
   3x = 165
    x = 165÷3
    x = 55
So William is 55 years old now.