The GCD of given numbers is 108.
Step 1 : Find prime factorization of each number.
$$\begin{aligned}756 =& 2\cdot2\cdot3\cdot3\cdot3\cdot7\\[8pt]324 =& 2\cdot2\cdot3\cdot3\cdot3\cdot3\\[8pt]540 =& 2\cdot2\cdot3\cdot3\cdot3\cdot5\\[8pt]\end{aligned}$$(view steps on how to factor 756, 324 and 540. )
Step 2 : Put a box around factors that are common for all numbers:
$$\begin{aligned}756 =& \color{blue}{\boxed{2}}\cdot\color{red}{\boxed{2}}\cdot\color{Fuchsia}{\boxed{3}}\cdot\color{Orange}{\boxed{3}}\cdot\color{Purple}{\boxed{3}}\cdot7\\[8pt]324 =& \color{blue}{\boxed{2}}\cdot\color{red}{\boxed{2}}\cdot\color{Fuchsia}{\boxed{3}}\cdot\color{Orange}{\boxed{3}}\cdot\color{Purple}{\boxed{3}}\cdot3\\[8pt]540 =& \color{blue}{\boxed{2}}\cdot\color{red}{\boxed{2}}\cdot\color{Fuchsia}{\boxed{3}}\cdot\color{Orange}{\boxed{3}}\cdot\color{Purple}{\boxed{3}}\cdot5\\[8pt]\end{aligned}$$Step 3 : Multiply the boxed numbers together:
$$ GCD = 2\cdot2\cdot3\cdot3\cdot3 = 108 $$This solution can be visualized using a Venn diagram.
The GCD equals the product of the numbers at the intersection.