Since the <em>bases</em> must not be painted, their areas are <em>not included</em> in the calculation.
The <em>surface</em> to paint, of each pillar, is equal to the lateral area of a<em> cylinder </em>with he dimensions given.
The formula for the laeral area of a cylinder is:
Substitute including the conversion factor to convert inches to feet:
Since the new phone can last 60% Longer than 4.2 hours, we multiply 4.2 by .6 and then add it back to 4.2
4.2 X 60% = 2.52
Therefore, the new phone can last 6.72 hours
The way it is written, none of them.
The "a"s cancel out.