(0.75×42.6-0.574×25+57.4）÷3
=(0.75×42.6-57.4×0.25+57.4）÷3
=(0.75×42.6+(1-0.25)×57.4）÷3
=(0.75×42.6+0.75×57.4）÷3
=(0.75×(42.6+57.4)）÷3
=0.75×100÷3
=75÷3
=25