Rita is saving up 15,000 to put a down payment on a condominium. if he starts with 8,000 saved and saves an additional $850 each month, which equation

I think there is more to the question, but the equation to solve for the number of months until Rita has enough money to put a down payment for a condominium is 15,000=8,000+850X

X= 2 he can buy 2 packs of cards for $12 and an action figure for $3 so he would spend $15 in total plus the free poster