Hey there!
4x - 9 = 15
ADD 9 to BOTH SIDES
4x - 9 + 9 = 15 + 9
CANCEL out: -9 + 9 because it gives you 0
KEEP: 15 + 9 because it help solve for the x-value.
NEW EQUATION: 4x = 15 + 9
SIMPLIFY IT!
4x = 24
DIVIDE 4 to BOTH SIDES
4x/4 = 24/4
CANCEL out: 4/4 because it gives you 1
KEEP: 24/4 because it gives you the answer of the x-value
NEW EQUATION: x = 24/4
SIMPLIFY IT!
x = 6
Therefore, your answer is: x = 6 (Option D.)
Good luck on your assignment and enjoy your day!
~Amphitrite1040:)