12 Oz sundae is $4.20
The cost is given by the following eqation
[tex]c=\frac{\text{Last time price}}{\text{Last time weight}}\cdot w[/tex]where,
c is the cost of the sundae
w is the weight of the sundae
last time price = $4.20
last time weight = 12 Oz
Solving:
[tex]c=\frac{4.20}{12}\cdot w[/tex]Simplify
[tex]c=0.35\cdot w[/tex]if the sundae is 17 Oz , then the price would be: $5.95
[tex]c=0.35\cdot17=5.95[/tex]