S=y-c means s = y-(100+0.8y) = 0.2y-100.
I=s is 0.2y- 100= 150-6r.
Get: r=250/6- 1/30y.
LM curve: LM curve means money demand = money supply.
L 1=L2, namely 0.2y-4r= 150.
Get: r =-37.5+0.05 y.
When the commodity market and the money market reach equilibrium at the same time
250/6- 1/30y=-37.5+0.05y
Get: y=950
r= 10%