应该是2.8×7.2×5.1÷2.8÷3.6÷5.1吧?
2.8×7.2×5.1÷2.8÷3.6÷5.1
=2.8÷2.8×5.1÷5.1×7.2÷3.6
=1×1×7.2÷3.6
=7.2÷3.6
=2