Let the yellow corn be x
And other variety be y
Question says that she brought a dozen (as total)
So,
x +y = 12
If cost of yellow corn was 40 cent and cost of other varieties were 50 cents then,
(After changing those cents into dollar)
0.40x+ 0.50y = 5.70
Because she paid a total of 5 dollar 70 cents for yellow and other variety.
So, option "a" is correct.
