i) 720:[41-(2x-5)] = 23.5
720: (41-2x+5)= 115
46 -2x =$\frac{144}{23}$
2x = $\frac{914}{23}$
x= $\frac{457}{23}$
Vậy x= $\frac{457}{23}$
m) 7x - x = $5^{21}$ : $5^{19}$ + 3. 2²- $7^{0}$
6x= 5² +3.4-1
6x= 25+12-1
6x=36
x=6
Vậy x=6
n)7x - 2x = $6^{17}$ : $6^{15}$ + 44 : 11
5x= 6² +4
5x =36+4
5x=40
x=8
Vậy x=8