You need to buy the supplies to carpet a 15 foot by 14 foot room. the padding costs $0.89 per square foot and the carpeting costs $2.99 per square foot. you also need tack strips to go around the perimeter of the room that cost $0.19 per foot.

So basically, you find the total time required to complete the item, by addition of time taken by task A, task B, and task C - 

TASK A - 2 and a half minutes is 2 minutes 30 seconds, which is 2(60) + 30 seconds = 120 + 30 = 150 seconds. 

TASK B - 3 minutes 10 seconds, which is 3(60) + 10 = 190 seconds 

LAST TASK - 1 minute = 1(60) = 60 seconds 

add them up --- 150 + 190 + 60 = 400 seconds 

Divide by 60 --- 400/60 = 40/6 = 20/3 minutes. 

Now, 1 item takes 20/3 minutes. 

let 'x' number of items take 25 minutes. 

Therefore, divide (25)/(20/3) = (25*3)/20 = 15/4 = 3.75