Explanation:

Let Asma's age
So, the age of grandfather of Asma   =  80 − x
The age of Asma after 10 years will be  = x + 10
So, the age of grandfather of Asma   = 80 − x + 10 = 90 − x
As per the condition is given in the question,

           90 − x

⇒ x + 10 = 4

⇒ 4x + 40 = 90 − x
⇒ 4x + x = 90 − 40 = 50

             50

⇒ x = 5 = 10
Hence, Asma's current age =10 Years.