Question

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

Answer 1

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.