Question 673179
let x = Krystal's age now
Jenny is three times as old so Jenny's current age = 3x

Jenny's age 4 yrs ago = 3x - 4
Krystal's age 4 yrs ago = x-4

four years ago she was four times as old as Krystal
3x-4 = 4(x-4)
       multiply by 4
3x-4 = 4x-16
add 16 to both sides
3x+12 = 4x
subtract 3x from both sides
12 = x

Krystal's age now is 12
Jenny's age now is 3(12) = 36

check work:
3x-4 = 4(x-4)
3(12)-4 = 4(12-4)
36-4 = 32
32=32