design 15 game thumbnails

I need someone to design 15 game thumbnails to replace the ones I have done myself. You can see the current versions on [login to view URL] under the section titled "our typing games". The designs should appeal to young adults still look professional. Ideally, applicants will make one sample to show me their vision as I don't intend to provide much other guidance, and I am looking for someone that can do this competently on their own and I won't be too picky about it as long as it meets the above criteria.