The number of bags of birdseed is "b" and each costs 4.09, then the cost of the "b" birdseed is 4.09b.
Next, the bags of millet is "m" and each cost 26, then the cost for "m" bags of millet is 26m.
Finally, the total of the order is obtained adding both:
Hence the answer is the first option, 4.09b+26m