My current age is 4 times what my sister's age was 20 years ago. i am now twice as old as i was 20 years ago. ten years ago, my sister's age was 1/2 of my current age. ten years ago, my age was 1.5 times my sister's age. what is my current age?

Let y = your current age
Let s = sister's current age
:
Write an equation for each statement, simplify as much as possible:

"my current age is 4 times what my sisters age was 20 years ago."
y = 4(s-20)
y = 4s - 80

" I am now twice as old as i was 20 years ago."
y = 2(y-20)
y = 2y - 40
40 = 2y -y
y = 40 yr, your present age

Right here you know enough to solve this
40 = 4s - 80
40 + 80 = 4s
s = 120/4
s = 30 is the sisters age