An interior beam with a rectangular cross section $450mm$ in height and $250mm$ in width is to be reinforced with $15M$ bars. The concrete has a compressive strength of $30$MPa and the steel has a tensile strength of $400$MPa. What are the maximum and minimum number of bars that could be used before risking brittle fracture? Assume one layer of reinforcement for this question. $($Hint: Find max and min area of reinforcement first.$)$