Alex spent 3/7 of his money he gave 1 / 4 of the remainder to his sistet he haf $120 left how much money did he in the beginning

Let his total money be x.

He spent (3/7) * x of his money.

He gave 1/4 (x-3/7x) to his sister.

which is : (1/4) * (4/7) * x = (1/7) * x

Now,

How much money he have in the beginning =

(3/7) * x + (1/7) * x+120=x

(4/7) * x+120=x

120=x - (4/7) * x

120 = (3/7) * x

x=120*7/3 [cross multiplication]

x=280.

So, Alex had $280 in the beginning.