



 
Hi, In the formula $V = \pi \; r^2 h$ you know $h = 15$ cm and $V= 1200$ cubic centimeters. Thus you have \[1200 = \pi \; r^2 \times 15.\] For part a) I would divide both sides of the equation by $15 \pi$ and then take the square root. The equation above can be rewritten as \[0 = \pi \; r^2 \times 15  1200\] and hence if you graph the function \[y = \pi \; r^2 \times 15  1200\] the graph will cross the raxis at the value that corresponds to $y = 0.$ I hope this helps,  


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