If you're calculating how much exercise she does in a week, we can break it down into simpler questions.
Firstly, how much does she exercise per day? Well, since she's walking on the outside of the field (assumingly), she would be walking around the perimeter of the field. So, Stacy would walk 2(80 +115) = 390 paces per day.
She exercises three days each week, so each week, Stacy would be walking 1170 paces per week.
