A gardener buys two kinds of fertilizer. Fertilizer A contains 60% filler materials by weight and Fertilizer B contains 40% filler materials by weight. Together, the fertilizers bought by the gardener contain a total of 240 pounds of filler materials. Which equation models this relationship, where x is the number of pounds of Fertilizer A and y is the number of pounds of Fertilizer B?
A) 0.4x + 0.6y = 240
B) 0.6x + 0.4y = 240
C) 40x + 60y = 240
D) 60x + 40y = 240