If the expression ax(2x + y - 5) simplifies to 6x² +3xy - 15x, what is the value of a?

65 8 7 4 5 6 8 4 3 2 1 9 5 6 4 2 1 6 5 1 5 1 3 2 3 5 multiply the third number in the first row by the seventh number in the third row. add this result to the fifth number in the second row. add to this total ten times the fourth number in the third row. subtract the eighth number in the first row from the result.

What is best way to getting answer for my exam is

Which property was used to simplify the expression? 3c+9 +4c=3c+4c+9