(x-3 целых 13 двадцать первых)+ 2 целых 10 двадцать первых= 7 целых 2 двадцать первых

[latex](x-3 \frac{13}{21}) +2 \frac{10}{21} =7 \frac{2}{21} \\ x-3 \frac{13}{21}=7 \frac{2}{21}-2 \frac{10}{21}\\ x-3 \frac{13}{21}=6 \frac{23}{21} -2 \frac{10}{21}\\ x-3 \frac{13}{21}=4 \frac{13}{21}\\ x=4 \frac{13}{21}+3 \frac{13}{21}\\ x=7 \frac{26}{21} =8 \frac{5}{21} \\ x=8 \frac{5}{21}. [/latex]