## Algebra 1: Common Core (15th Edition)

$a=-\frac{1}{21}$
First we need to subtract $\frac{1}{3}$ from both sides to isolate the variable: $\frac{2}{7}-\frac{1}{3}=\frac{1}{3}-\frac{1}{3}+a$ In order to go further, we must find a common denominator to subtract the fractions. The quickest way to find a common denominator is to multiply the two denominators together; $7*3=21$: $\frac{2}{7}*\frac{3}{3}=\frac{6}{21}$ and $\frac{1}{3}*\frac{7}{7}=\frac{7}{21}$ Now we can substitute those new fractions in our equation so we can subtract them $\frac{6}{21}-\frac{7}{21}=a$ When subtracting fractions, you subtract the numerators but you keep the denominator the same $-\frac{1}{21}=a$