Lego is liked by children as well as adults. Management at a lego company wonders if lego sets purchased for adults are on average more expensive than than lego purchased for children (because lego sets liked by adults are often more expensive). So management collects a random sample of 49 lego sets purchased for children and 39 sets purchased for adults (buyers are interviewed). They find that on average, $60 was spent on lego sets purchased for children, with a standard deviation of $15.64. Whereas, lego sets purchased for adults were on average $85 with a standard deviation of $11.68. So management wants to investigate if HA: ac>0, where a represents adults and c represents children. 

What is the standard error for the difference between sample means for money spent on lego between the adults group and the children group SE(yayc)?