1) 5300 * a + 4200 * b = 5300 * 50 + 4200 * 90 = 265000 + 378000 = 643000

2) 720 * a - 360 * b = 720 * 700 - 360 * 80 = 504000 - 28800 = 475200

5300*50+4200*90=

5300*50=265000

4200*90=378000

265000+378000=643000

720*700-360*80=

720*700=504000

360*80=28800

504000-28800=475200