A farmer spent $35 on feed for chickens and goats. He spent 40% money on chicken feed, which he bought at a 20% discount off the full price, and spent the rest on goat feed, which he bought at full price. If the farmer had paid full price for both the chicken feed and the goat feed, what amount would he have spent on the chicken feed and goat feed combined?

A. $37.80

B. $38.50

C. $39.20

D. $39.50

E. $40.60

I set up the equation as follows: (C for chicken feed and G for goat feed)

0.8x0.4xC + 0.6G =35---a

0.4C+0.6G=35+?----b

equation b is 8% greater than a so I multiplied 35 by 8%, getting $2.8. Thus, I selected 37.8 but the answer is 38.50.

Q: could anyone please kindly point out what went wrong here?

The OA explanation is as follows but I can't understand the part in bold

0.4($35)=F (full price of chicken feed)

$14=0.8F$17.5=F

Total paid = 17.5+35(0.6)=38.50

Q: how can 14=F and then change to 14=0.8F?

Many thanks!!