a, $100$ - $7.( x - 5 )$ = $58$
$7.( x - 5 )$ = $100$ - $58$
$7.( x - 5 )$ = $42$
$x$ - $5$ = $42$ : $7$
$x$ - $5$ = $6$
⇒ $x$ = $11$
b, $12( x - 1 )$ : $13$ = $4³$ + $2³$
$12( x - 1 )$ = $( 64 + 8 )$ . $13$
$12( x - 1 )$ = $72$ . $13$
$12( x - 1 )$ = $936$
$x$ - $1$ = $936$ : $12$
$x$ - $1$ = $78$
⇒ $x$ = $79$
c, $24$ + $5x$ = $7^{5}$ : $7³$
$5x$ = $7²$ - $24$
$5x$ = $49$ - $24$
$5x$ = $25$
⇒ $x$ = $5$
d, $5x$ - $206$ = $2^{4}$ . $4$
$5x$ = $2^{4}$ . $4$ + $206$
$5x$ = $64$ + $206$
$5x$ = $270$
⇒ $x$ = $54$
