Write the equation making substitutions for known values: 16 1/2=(22/7)(r+2). If we multiply by 2 all the way through we'll get rid of the fraction: 33=(44/7)(r+2). We still have 7 from pi so multiply through by 7 and expand the brackets: 231=44r+88. Subtract 88 from each side: 143=44r. Divide through by 11: 13=4r, so 4r=13 and r=13/4=3 1/4.