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