1)) 3целых1\4+6,4-7,52)) (21,3-18целых3\4)/3,43)) 2\11*(14целых1\3+2целых1\6)4))...

$1) 3 \frac{1}{4} + 6,4-7,5= 3,25+6,4-7,5= 9, 65-7,5= 2,15$
$2) \frac{21,3-18 \frac{3}{4} }{3,4} = \frac{21,3-18,75}{3,4} = \frac{2,55}{3,4} =0,75$
в скобочках приводим к общему знаменателю $\frac{2}{11} *(14 \frac{1}{3} +2 \frac{1}{6} )= \frac{2}{11} *( \frac{43}{3} + \frac{13}{6})= \frac{2}{11} *( \frac{86}{6} + \frac{13}{6} )=\frac{2}{11} *\frac{99}{6} = \frac{2*99}{11*6} =$ $= \frac{2*33}{11*2} = \frac{33}{11} =3$
$4)(5\frac{1}{6} -3,25)*\frac{4}{23}=(\frac{31}{6}-3 \frac{1}{4})*\frac{4}{23}=(\frac{31}{6}-\frac{13}{4})* \frac{4}{23}=(\frac{62}{12}-\frac{39}{12})*\frac{4}{23}= \\ \frac{23*4}{12*23} = \frac{1}{3}$