In the "I was told there would be no math" department...
On your current rates, your rate per hour decreases as session time goes up:
30 min = $1/min
60 min = .83/min
90 min = .78/min
If you raise your hourly rates a flat amount ($10), then it shifts those relationships.
If you want to keep the same relationship, then the new rates would be something like:
30 min - $36/hr
60 min - $60/hr
90 min - $84/hr