A rectangular farm has to be fenced on one long side, one short side and the diagonal. If the cost of fencing is Rs. 100 per m, the area of the farm is 1200 m² and the short side is 30 m long, how much would the job cost ?

Length :
$$\eqalign{ & = \left( {\frac{{1200}}{{30}}} \right)m \cr & = 40\,m \cr} $$
Diagonal :
$$\eqalign{ & = \left( {\sqrt {{{\left( {40} \right)}^2} + {{\left( {30} \right)}^2}} } \right)m \cr & = 50\,m \cr} $$
Length to be fenced :
$$\eqalign{ & = \left( {40 + 30 + 50} \right)m \cr & = 120\,m \cr} $$
∴ Cost of fencing :
$$\eqalign{ & = {\text{Rs}}{\text{.}}\left( {120 \times 100} \right) \cr & {\text{ = Rs}}.12000 \cr} $$