Write the molecular formula for a compound with the possible elements C, H, N and O that exhibits a molecular ion at M+ = 84.095 I understand the concept of adding together the specific mass C=12.000,

Write the molecular formula for a compound with the possible elements C, H, N and O that exhibits a molecular ion at M+ = 84.095

I understand the concept of adding together the specific mass C=12.000, H=1.008, N=14.003 and O=15.995 but I need help with a systematic approach to solve for these problems when that is the only information that is given.