Question 936901
let x,y be the present ages of Mr. alvarado and his sons
  Mr. alvarado is 20 years older than his son.
 hence  
                    x= y+20..........eq(1)
In years , alvarado age will be  = x+5
              his son's age  = y+5
 In 5 years, he will be 5 years more than twice as old as his son 
              (x+5)= 2(y+5)+5
 x+5 = 2*y+2*5 +5
 x+5 = 2y+10+5
 x+5= 2y+15
   x= 2y+10
    but x= y+20 from eq(1)
   2y+10  =y+20
      2y-y+10 =20
         y+10 = 20
              y= 10 
  present age of son  = 10
 present age of alvarado  =  10+20  =30  years