a) 720 : ( 41 - x ) = $2^{3}$ . 5
720 : ( 41 - x ) = 8 . 5
720 : ( 41 - x ) = 40
41 - x = 720 : 40
41 - x = 18
x = 41 - 18
x = 23
b) (5x - 4 ) : 2 = $2^{3}$
(5x - 4 ) : 2 = 8
5x - 4 = 8 . 2
5x - 4 = 16
5x = 16 + 4
5x = 20
x = 20 : 5
x = 4
c) $3^{x}$ = $3^{2}$ . 27
$3^{x}$ = 9 . 27
$3^{x}$ = 243
$3^{x}$ = $3^{5}$
⇒ x = 5
d) $5^{3}$. $5^{x-2}$ = $25^{2}$
$5^{3}$. $5^{x-2}$ = ($5^{2}$)$^{2}$
$5^{3}$. $5^{x-2}$ = $5^{4}$
⇒ 3 . x - 2 = 4
3 . x = 4 + 2
3 . x = 6
x = 6 : 3
x = 2