58. If \( a+b+c=10 \) and \( a^{2}+b^{2}+c^{2}=36 \) then, \( a b+b c+c a \) is \( \begin{array}{ll}\text { (a) } 32 & \text { (b) } 64 \\ \text { (c) } 68 & \text { (d) } 136\end{array} \)

s of ' \( a \) ' and ' \( b \) ', for which the equations \( 3 x-(a-1) y=b+7,6 x-(a+4) y=5 b-1 \) infinite solutions, are

4. (20б) Решите систему \( \left\{\begin{array}{c}2 z_{1}-3 i z_{2}=3 i \\ (3-2 i) \cdot z_{1}-i z_{2}=1+2 i\end{array}\right. \)

Simplify \( \frac{3}{4}+\frac{2}{3}(9 x+6)+4 x+3 \frac{1}{4} \)

Решите систему неравенств. \( \left\{\begin{array}{l}4 x>0 \\ \frac{1}{5} x \geq-1\end{array}\right. \) Ваш ответ:

Write a simplified algebraic expressions for the phrase "two thirds of the difference of \( x \) from \( y \) adided to twice \( x \).