Assuming Sarah travelled in a constant speed

she travelled 15 miles in 2 hours, so 15/2= 7.5 so she goes 7.5 miles per hour

each miles is 1760 yards, 1760*7.5= 13200 yard

so we know that she travelled 13200 yards in an hour, there are 60 mins in an hour

applying the equation distance/time = speed

we get 13200/60 = 220

so she travels 220 yards every mins