The ratio of the number of boys to the number of girls in a class is 5 to 7. How many boys are there if there are 21 girls?

Which two properties of equality could zoe use to finish solving for x? the equation is 3x - 4 = -10 for x so a either the addition or subtraction property of equalityb ether the multiplication or division property of equality c ether the addition or division property of equality d ether the subtraction or division property of equality just a simple a b c or d plz.