Answer:
[tex]200 \ marbles[/tex]
Step-by-step explanation:
[tex]Let\ Alan\ have\ =x\ marbles\\Brady\ have = (x+20)\ marbles\\Matt\ have = . (x+120)\ marbles\\\\Total\ marbles = 740\\x+(x+20)+(x+120)=740\\x+x+20+x+120=740\\3x+140=740\\3x=740-140\\3x=600[/tex]
Dividing [tex]3[/tex] both sides.
[tex]\frac{3x}{3}=\frac{600}{3}\\\\x=200[/tex]