Daisy spent a total of $31 before tax on ice cream. the table below shows the different flavors she bought. a carton of strawberry ice cream costs $1.50 more than a carton of vanilla ice cream. which system of equations can be used to calculate s, the cost before tax for 1 carton of strawberry ice cream, and v, the cost before tax for 1 carton of vanilla ice cream?

The cost of 1 vanilla ice cream and 1 strawberry ice cream should total to $31. Since you only bought one of each flavor, you simply have to add their unit prices. 

Cost for 1 carton of strawberry ice cream + Cost for 1 carton of vanilla ice cream = Total Cost
Total Cost = s + v  --> this is the general equation

Since s = 1.5 + v, the modified equation would be
Total Cost = 1.5 + v + v
Total Cost = 1.5 + 2v