a) $541 + (218 – x) = 735$

<=> $218 – x = 735 – 541$

<=> $218 - x = 194$

<=> $x = 218 – 194$

<=> $x = 24$

Vậy $x = 24$.

b) $5(x + 35) = 515$

<=> $x + 35 = 515:5$

<=> $x + 35 = 103$

<=> $x = 103 – 35$

<=> $x = 68$

Vậy $x = 68$.

c) $96 – 3(x + 1) = 42$

<=> $3(x + 1) = 96 - 42$

<=> $3(x + 1) = 54$

<=> $x + 1 = 54:3$

<=> $x + 1 = 18$

<=> $x = 18 - 1$

<=> $x = 17$

Vậy $x = 17$.

d) $12x – 33 = 3^{2}.3^{3}$

<=> $12x - 33 = 9.27$

<=> $12x - 33 = 243$

<=> $12x = 243 + 33$

<=> $12x = 276$

<=> $x = 276:12$

<=> $x = 23$

Vậy $x = 23$.