Josie's hair currently falls about 16 centimeters (\text{cm})(cm)left parenthesis, start text, c, m, end text, right parenthesis below her shoulder and grows about 5\text{ cm}5 cm5, start text, space, c, m, end text every 4 months. Josie plans to grow her hair and donate about 21\text{ cm}21 cm21, start text, space, c, m, end text of her hair to charity after her next haircut. If Josie would like to have her hair fall about 5\text{ cm}5 cm5, start text, space, c, m, end text below her shoulders after her next haircut, which of the following equations could be used to find the number of months, mmm, for which Josie must grow her hair?