1.) Define your variables
x= number of coats that must be sold (quantity)
2.) Set up your equations
Revenue= price * quantity = 175 * x
Cost = variable cost + fixed cost = 71.50x +45000
Profit = revenue - cost = 175x - (71.50x + 45000) = 175x -71.50x - 45000 = 3000
3.) Solve the profit equation for x
175x - 71.50x - 45000 = 3000
I'll let you finish the equation.