Nasir travel $$ 3 \dfrac {1}{2} km $$ in bus = $$ \dfrac {7}{2} km $$
Walked $$ 1 \dfrac {1}{8} km $$ to reach a town = $$ \dfrac {9}{8} km $$
$$ \therefore $$ Total distance covered by nasir
$$ \Rightarrow ( \dfrac {7}{2} + \dfrac {9}{8}) km = \dfrac {( 7 \times 8) +( 9 \times 2) }{2 \times 8} km = \dfrac { 56 + 18 }{16} km $$
$$ \Rightarrow \dfrac {74}{16} km = \dfrac { 74 \div 2 }{ 16 \div 2}km =\dfrac {37}{8} km = 4 \dfrac {5}{8}km $$