The formula for the area of a trapezoid is A=1/2(base one+base two)h
All you have to do is find the base one, base two, and height using the given information and then plug it into the equation.
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
Your thinking of the number 69