Solution:

Wilfred will turn both the 4-min hour glass and 7 min hour glass together so now after 4 min there will be 3 min available in the 7min hour glass now at this point he will again turn both of them upside down. Now after 3 min the 7 min hour glass will finish so wilfred will turn it upside down again at this point 7 min have passed and 3 min have passed in 4 min hour glass so by the time another min passses the 4 min hour glass will end completely and in the 7 min hour glass only one min has passed so he will turn 7 min hour glass upside down and hence after 1 min it will end and hence he can successfully measure 9 min :) hurray wilfred wins :) : )