Working at their respective constant rates, machine A makes 100 copies

1 hour = 500 copies (Machine A)
2 hours = 1000 copies


1 hour = 400 copies (Machine B)
2 hours = 800 copies

Together they make 1800 copies per hour.

1) X=Y but what no. Of machines are working together?
1800, 3600, 5400 or more?
No idea.
(Insufficient)

2) 5x+4y = 90

X = 2 , Y = 20
Copies to be manufactured = 1000*2+20*800 = 2000+16000 = 18000

6 = X, Y = 15
Copies to be manufactured = 1000*6+15*800 = 6000+12000 = 18000

X = 10, Y = 10
Copies to be manufactured = 1000*10+10*800 = 10000+8000 = 18000

X = 14 , y = 5
Copies to be manufactured = 1000*14+5*800 = 14000+4000 = 18000

X = 18, Y = 0
Copies to be manufactured = 1000*18+0*800 = 18000

Manufactured copies no. Are same.
(Sufficient)

Answer is B

Posted from my mobile device