To earn back the amount Helen spent on certification, she would need to earn $90. Since her base salary is $55 per month, she would need to teach an additional $90 - $55 = $35 in classes. Since she earns $5 per class, she would need to teach $35 / $5 = 7 classes.
So, Helen will need to teach 7 classes to earn back the amount she spent on certification.
Her total earning for teaching 7 classes would be $55 (base salary) + $5 (per class) * 7 (classes) = $110
Therefore Helen's expenses and earning would be $90 (certification cost) and $110 (earning) respectively.