I have found that when working on a math mission on a mobile browser (Android), I am sometimes not able to type anything into the answer box. I suspect it happens with answer boxes that have options for special characters like square root, pi, etc. I have included a screen shot of an answer box I could not type in. I don't have this problem when using the app, but I like to use the browser version since the app does not track mission progress or have mastery challenges. Thanks!