12 boys. 7 * 3 is 21. 21 girls. 4*3 is 12. 12 boys 21 girls
Z = -2/3a
divide by -2/3 on both sides
a = z divided by -2/3
a = -3/2z
8 = 4w/3 Original Problem.
4w/3 = 8 Flip Flopped the problem around.
4w = 24 Multiplied each side by 3.
w = 6 Divided each side by 4.
Answer: w = 6
I have memorized facts about fractions like these, so can tell you ...

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A fraction with 9 as a denominator is a repeating 1-digit decimal with the decimal digit being the numerator of the fraction.
A fraction with 11 as a denominator is a repeating 2-digit decimal with the two digits being 9 times the numerator of the fraction.
1/8 = 0.125, so any multiple of 1/8 is that multiple of 0.125.