how to add -std=c++11 to make file

I want to add -std=c++11 to my makefile but I do not Where to add, here is my code:

hw07: test.o functions.o
    g++ test.o functions.o -o hw07
test.o: test.cpp headerfile.h
    g++ -c test.cpp
functions.o: functions.cpp  headerfile.h
    g++ -c functions.cpp
clean:
    rm *.o hw07

in the above code where should I add the stdc++11 code, please help me out about...