What is net present value (NPV) how is it calculated and what is the basic premi

What is net present value (NPV) how is it calculated and what is the basic premise of its decision rule?What is the internal rate of return (IRR) how is it calculated and what is the basic premise of its decision rule?What is the modified internal rate of return (MIRR) how is it calculated and what is the basic premise of its decision rule?