Esther spent 18 of her money on a shirt and 4 sweaters. The shirt cost 2 times as much as each sweater. Esther spent 23 of her remaining money on a necklace. She spent $576 more on the necklace than on the 4 sweaters.
(a) What fraction of Esther's money was spent on each sweater?
(b) How much money did Esther have at first?