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What is the approximate surface area of a cylinder that has a radius of 6 centimeters and a height of 15 centimeters? 

Approximate?  3 times 12 is 36, then that times 15 which is 360 + 18 = 540

and then just a little more because pi is a little more than 3.  Call it 550 cm².  

Calculated:  3.14 • 12 • 15 = 565 cm². 

Hmmm, my approximation wasn't bad.  Not real good, but not bad. 

_.

Two end caps        +      lateral surface area

    pi r^2 *2             +      pi * d * h

pi (6^2) * 2            +      pi * 12 * 15

pi ( 72 + 180)

791.68 cm²