Question

Alex and Benny had 440 cards. Alex and Cruz had 320 cards. Benny had 3 times as many cards as Cruz. How many cards did Alex have?

Answer 1

260 cards. 

Process: 
A = Alex
B = Benny
C = Cruz

a+b=440
a+c=320

a=440-b
a=320-c

a=440-b=320-c

b=3c

a=440-(3c)=320-c
-3c+440 = -c+320
-3c=-c-120
-2c=-120
c=60

a=320-c
a=320-60

a=260