`a`, $5^{6}$ : $5^{4}$ + $2^{3}$ . $2^{2}$ - $1^{2021}$
$=$ $5^{2}$ + $2^{5}$ $-$ $1$
$=$ $25 + 32 - 1$
$=$ $56$
`b`, $94 . 12 + 12 . 5 + 12$
$=$ $12.(94 + 5 + 1)$
$=$ $12. 100$
$=$ $1200$
`c`, $[1200 - (4² - 2.3)³]: 40$
$=$ $[1200 - (16 - 6)³]: 40$
$=$ $[1200 - 10³]: 40$
$=$ $200 : 40$
$=$ $5$
d, $360 - 3{[655-(18: 2 + 1).4³ + 5]}: 10^{0}$
$=$ $360 - 3{[655-10].64+ 5]}: 1$
$=$ $360 - 3.{645.64+5}: 1$
$=$ $360 - 3. 41285 : 1$
$=$ $-123495$
