6.72 : (203.2 -х)=2.1 1.3х+3.8х-0.03=2.01

I) 1.3х + 3.8х-0.03=2.01 

1.3х + 3.8х = 2.01 + 0.03
5.1х = 2.04
х = 2.04/5.1
х = 0.4
Проверка:
5.1 * 0.4 = 2.04
2.04 = 2.04
ответ: х=0.4

II) 6.72/(203.2 -х)=2.1

203.2 - x = 6.72/2.1
203.2 - х = 3.2 
х = 203.2 - 3.2
х = 200
Проверка:
6.72/(203.2 - 200) = 2.1
6.72/3.2 = 2.1
2.1 = 2.1
ответ: х=200