Question 610773
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Hi, 
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Surface Area = Area of Base + lateral Area
 550 = {{{pi*r^2 + pi*r*s}}} where s is the slant height
 550/3.14 = {{{r^2 + 25r}}} or
 r^2 + 25r - 175.1 = 0
{{{r = (-b +- sqrt( b^2-4*a*c ))/(2*a) }}}
{{{r = (-25 +- sqrt( 1325.4 ))/(2) }}}
   r = 5.7 units     (tossing out negative solution for length)