Revenue rises straight with every billable hour; total cost starts at the fixed overhead and rises with the variable cost per hour. Where the two lines cross is the break-even point — below it you lose money, above it profit grows linearly. The horizontal axis is billable hours per month; each consultant can bill at most 8 hours × 22 days = 176 hours a month.
R(h) = rate · h · Total cost: C(h) = fixed + varCost · h · Profit: π(h) = (rate − varCost)·h − fixedh* = fixed / (rate − varCost) · Capacity: consultants × 176 billable hours / month