Grayson Enterprises manufactures springs and shock absorbers. Springs account for 40% of the company's total sales revenue, whereas shocks account for about 60%. The contribution margin ratios for springs and shocks are 45% and 35%, respectively. Grayson's fixed costs average $450,000 per month.

In order to earn an operating income of $252,000, Grayson's monthly sales must be:

a. $1,700,000

b. $1,750,000

c. $1,800,000

d. $1,850,000