In response to complaints about high prices, a grocery chain runs the following advertising campaign: $$If you pay your child $$7$ to go buy $$50$ worth of groceries, then your child makes twice as much on the trip as we do$.$ You$$ve collected the following information from the grocery chain$$s financial statements:

$($in millions$)$

Sales $ $500\mathrm{.}0$

Net income $35\mathrm{.}0$

Total assets $510\mathrm{.}0$

Total debt $380\mathrm{.}0$

a$.$ What is the profit margin for the child as a percentage of what they spend and the profit margin for the store? $($Do not round intermediate calculations and enter your answers as a percent rounded to $2$ decimal places, e$.$g$.,32\mathrm{.}16.)$

b$.$ What is the store's ROE? $($Do not round intermediate calculations and enter your answer as a percent rounded to $2$ decimal places, e$.$g$.,32\mathrm{.}16.)$