2a^2b-[3a^2b-(3a^2c-a^2b)-2a^2c]
=2a^2b-3a^2b+(3a^2c-a^2b)+2a^2c
=-a^2b+3a^2c-a^2b+2a^2c
=-2a^2b+5a^2c
=-4-5/2
=-13/2