A mother is 21 years old then her new born daughter. how old does her daughter when her age will be 1 by 4 of her mother

Answer 1

Trying to make sense out of the gibberish English.
I will assume you meant:
How old will her daughter be when her age is 1/3 of her mother's age.

daughter now : ---- 0
mother now -------21

0+x = (1/4)(21+x)
4x = 21 + x
3x = 21
x = 7

Find their ages in 7 years, and see if your condition is met.