MR-877 / 12b. problem

Simplify the following expression:

25x+20x+16x·5x-4x

25x+20x+16x·5x-4x

=25x·5x+25x·-4x+20x·5x+20x·-4x+16x·5x+16x·-4x

=125x-100x+100x-80x+80x-64x

=125x-64x