I am trying to make a formula for staffing for my business.

Our minimum staffing in the store is 2 people
For every $50 in sales we need a person
if the sales are $150 we need 3
if the sales are $25 we still need

a1 Sales per man $50
a2 Sales 150
a3 People needed 3 (Formula a2/a1)

b1 Sales per man hour $50
b2 Sales $25
b3 People needed What is the formula?
(b2/b1 will give 1 - I need it to tell me atleast 2)

It seems to be an atleast or not less than but I do not know how to write it.
Can anyone give a simple solution?

Greatly appreciated!
JM