How do you do this? it's due tomorrow

Lets think they have cards,  Alex = x , Gil = y and Meg = z. Then,
x+y+z = 740

Alex had 20 fewer cards than Gil. So,
x+20 = y

Alex had 120 fewer cards than Meg. So,
x+120 = z

 x+(x+20)+(x+120) = 740
3x + 140 = 740
x= 200

y= 220
z= 320

So Alex had 200 cards, Gil had 220 cards and Meg had 340 cards

A=alex
g=gil
m=meg

they share 740 cards
a+g+m=740

alex has 20 fewer than gil and 120 fewer than meg (women rights?)
a=g-20 and a=m-120

so

a=g-20 and a=m-120
add 20 to bot sides for the left one and 120 to boht isdes for the right one
a+20=g and a+120=m

subsitute a+20=g for g and a+120=m for m

a+g+m=740
a+a+20+a+120=740
3a+140=740
minus 140 both sides
3a=600
divide both sies by 3
a=200

alex has 200 cards