$C_{1}(P_{1})=0.01P^{2}_{1}+30P_{1}+10 ; 100MW \leq P_{1}\leq 150MW$
$C_{2}(P_{2})=0.05P^{2}_{2}+10P_{2}+10 ; 100MW \leq P_{2}\leq 180MW$
The incremental cost (in Rs/MWh) of the power plant when it supplies $200$ MW is _______.