Which situation cannot be represented by this equation? x + 7 = 31 taliba has $31 to order phone cases online. she buys 4 phone cases and pays a $7 shipping charge. what is x, the cost of each phone case? taliba is ordering phone cases that cost $4 each online. there is also a $7 shipping charge. if she has $31 to spend, how many phone cases, x, can she buy? taliba has $31 to order phone cases online. each phone case costs $7, and there is a $4 shipping charge. how many phone cases, x, can taliba buy?