The total Kate spent was $45 on a jacket and $42 on boots for a total $87
The total Rosa spent was $27 on jeans, $22 on a sweater and an unknown amount of sneakers. The equation to model the word problem is as follows.
27+22+X=87 can be simplified to 49+X=87 and can be further simplified to X=38
Rosa spent $38 on the sneakers.