well the question specifically states that what are the possible combinations.. which clearly means there would be an infinite number of solutions..so after the reccomendation of your teacher, you can ask him/her if you could write just a few pairs..thats what i did...

## solution..

well the question specifically states that what are the possible combinations.. which clearly means there would be an infinite number of solutions..so after the reccomendation of your teacher, you can ask him/her if you could write just a few pairs..thats what i did...