6. Упростите выражение: $$\frac{5X}{7}$$+$$\frac{4}{21}$$ - $$\frac{2}{3}$$X

$$\frac{5X}{7}$$+$$\frac{4}{21}$$ - $$\frac{2}{3}$$X = $$\frac{5X*3}{7*3}$$+$$\frac{4}{21}$$ - $$\frac{2X*7}{3*7}$$ = $$\frac{15X}{21}$$+$$\frac{4}{21}$$ - $$\frac{14X}{21}$$ = $$\frac{15X+4-14X}{21}$$ = $$\frac{X+4}{21}$$

Ответ: $$\frac{X+4}{21}$$