15.83= 5.95+0.19x
x would be the number of photos. to solve you subtract 5.95 from both sides which gets you 9.88=0.19x. so next you divide both sides by 0.19 which gets you 52 meaning she bought 52 photos. you check by inputting the variable 15.83= 5.95+0.19(52) and when you perform the math it gets you 15.83=15.83 meaning your answer is correct. hope this helped :)
