A bath tub has 2 taps(hot and cold) and a waste pipe to let the water flow out. it takes the hot tap 10 minutes to fill the tub and it takes the cold tap 15 minutes to fill the tub and it takes the waste pipe 20 minutes to empty the tub when it is full. Both taps and waste pipe are opened to full capacity for water to flow. After 5 minutes, the waste pipe is closed. 2 minutes later the hot tap is closed. How much longer will it take the cold tap to fill the tub?

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