7. (10 points) Xiao Ming is preparing to make dumplings. He added 5 kilograms of water to 1.5 kilograms of flour and found the dough too runny. His grandmother told him that the dough for making dumplings should be mixed with 3 parts flour and 2 parts water. So, Xiao Ming added the same amount of flour three times, and finally, the dough was mixed as required. How many kilograms of flour did he add each time? $\qquad$ kilograms of flour.