The perpetuity is received in arrears mean at the end of year so we write it in time 1..And the P.V is calculated as..
20/.1=200*.909(we multiply because its in year 1 and we want in year zero)=181.8 Tax P.V=20*.3=6/.1=60*.826(Because tax is paid one year after so first tax is paid in time 3)=49.56 So the P.V of perpetuity is 181.8-46.56=132.24