Homozygous recessive yellow-bodied-echinus-white-eyed female

In fruit flies, the yellow-bodied (y), echinus (ec) and white-eyed (w) mutations are all recessive to their corresponding normal alleles. A homozygous recessive yellow-bodied, echinus, white-eyed female (y ec w / y ec w, the gene order is arbitrary) was mated to a normal male, and the resulting F1 females were mated to homozygous recessive males. After collecting 1000 F2 progeny, the following numbers were observed with each phenotype:
+ + + 475
y ec w 469
y + + 8
+ ec w 7
y + w 18
+ ec + 23
+ + w 0
y ec + 0
What is the genetic map distance from y to w?

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