workout doubt

[riyaf]

Can someone explain the answer to the following ?

6.5 Shirley Sixpack, as you will recall, thinks that two 8-ounce cans
of beer are exactly as good as one 16-ounce can of beer. Suppose that
these are the only sizes of beer available to her and that she has $30 to
spend on beer. Suppose that an 8-ounce beer costs $.75 and a 16-ounce
beer costs $1.
(c) What if the price of 8-ounce beers falls to $.40? How many 8-ounce
beers will she buy then?
 
The answer is 75 cans.
I got two equations : X1+ 2X2 = 150 & X1 + 2X2= 30 which don't yield any answers. Plz help !

[The Villain]

consumes only x2 and no units of x1 as p2 is less than p1.
thefore consumes m/p2=30/.4=75

(x1 is 2 eight ounce cans
n x2 is 16 once beer)

[riyaf]

Thanks a ton :)