Build an online assissment to students and they must be able to take test using their mobile

We are looking for a web application with Android development. The project is called, designing a Secure Exam Management. A web application with admin and student login. Admin must be able to add: Student database, Subjects and then Questions and answers for each subject. Upon setting these questions, he should be able to send an invite to all the database with a QR code. The students after receiving this email, must use the QR code to access their test papers on their mobile phone using android app. At a time if multiple candidate are taking up the same subject, then the students must get different test questions. End of the test, if the student still have time, must be able to go back and correct the test questions. Post this the student must get their results, like total questions assigned, questions answered, total correct answers and percentage. Let us know if anyone can take this assignment and if so, how much time will it take and what will be the cost for this project.