Question 975833
Volume of original is 8*12*4=384 cm^3
Increase the height 25% to 5 cm will increase the volume 25%, since it is linear
8*12*5=480 cm^3, and the increase (96 cm^3)/original amount, 480 cm^3 =20%

Volume of cylinder is area of circle *height.  It is 16cm^2*pi*8 cm and units will be cm^3
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To increase the volume 15%, since it is linear with height, increase the height 15%, to 9.2 cm

Original volume is 128*pi cm^3
New volume is 147.2 pi^cm^3

 The % increase is 19.2pi/128pi , and that is 15%.  

I didn't use 3.14 for pi, but that may be used. Answers in pi are reasonable unless there is a specific statement saying otherwise.  To the nearest hundredth "when necessary" I mean as not necessary here.