To solve this expression step by step:

Calculate 42^2: 42^2 = 42 x 42 = 1764Calculate 4^2: 4^2 = 4 x 4 = 16Subtract the result of 4^2 from the result of 42^2: 1764 - 16 = 1748Finally, multiply the answer by 6: 1748 x 6 = 10488

The final answer is 10488.