Hint: Here we go through by arranging the digits in the descending order because we have to find the greatest three digit number from the digits.
Complete step-by-step answer:
Here in the question the three digits are given i.e. 7, 6 and 3. We have to find out the greatest three digit number from the given digit.
As we know for finding the greatest digit number we should have to arrange the digits in descending order because we know that we have to put the greatest digit at a hundred value and then after the 2nd digit which is greater than the smaller one at tens place and at end the smaller digit at once place. By arranging the digit in descending order we get, 7>6>3. Now for roaming the number we write it as $7 \times 100 + 6 \times 10 + 3 = 763$
Hence option A is the correct answer.
Note: - whenever we face such a type of question the key concept for solving the question is you have knowledge of arranging the digits in descending order for greatest number and ascending for smaller number. You can easily find the answer by first seeing which option contains only the given three digit then find out which one is greatest to get our answer.