(5 2/9a+3 1/3)×3-7 2/3a если а=3 1/8

$(5\frac{2}{9} a + 3 \frac{1}{3} )*3- 7 \frac{2}{3} a= 15\frac{2}{3} a + 10-7 \frac{2}{3} a= 8a+10$

$a= 3 \frac{1}{8} \\ \\ 8*3 \frac{1}{8}+10= \frac{8*25}{1*8} +10= 25+10=35$

проверим на полном выражении:
$(5\frac{2}{9} *3 \frac{1}{8} + 3 \frac{1}{3} )*3- 7 \frac{2}{3} *3 \frac{1}{8}= \\ \\ = ( \frac{47*25}{9*8} + 3 \frac{1}{3} )*3 - \frac{23*25}{3*8} = \\ \\ =( 16 \frac{23}{72} + 3 \frac{1}{3} )*3 - \frac{575}{24} = \\ \\ = (16 \frac{23}{72} + 3 \frac{24}{72} )*3 - 23 \frac{23}{24} = \\ \\ = \frac{1415*3}{72*1} - 23 \frac{23}{24} = 58 \frac{23}{24} - 23 \frac{23}{24} = 35$