60 * 5 + 42/6 * 8 / 690 + (480 - 180) * 6 = 2100ц 28/345
1) 480 - 180 = 300
2) 60 * 5 = 300
3) 42/6 * 8 = 56
4) 300 * 6 = 1800
5) 56 / 690 = 56/690 = 28/345
6) 300 + 28/345 + 1800 = 2100ц 28/345
4 дм^2 + 829 мм^2 = 4 дм^2 + 0.0829 дм^2 = 4.0829 дм^2
8 дм^2 - 1700 мм^2 = 8 дм^2 - 0.17 дм^2 = 7.83 дм^2