A rectangular room is \( 2 \) times as long as it is wide, and its perimeter is \( 42 \) meters. Find the dimension of the room. The length is : \( 14 \) meters and the width is \( 7 \) meters. 

ii) \( (3-b)\left(9+3 b+b^{2}\right) \)

4. Coxhadlini vuruqlara ayırın: \( \begin{array}{ll}\text { a) } a^{3}-a^{2}+a-1 ; & \text { b) } x^{2}-x z-5 x+5 z \text {; } \\ \text { c) } b^{2}-8 b+12 ; & \text { d) } a(5-b)+8(b-5)\end{array} \)

\( \left\{\begin{array}{l}\text { (Q1; 2,6 балла) Решите систел } \\ x+y=3 \\ x^{2}-y^{2}=21\end{array}\right. \)

177. Mukul has \( \$ 3.75 \) in quarters, dimes and nickels in his pocket. He has five more dimes than quarters and nine more nickels than quarters. How many of each coin are in his pocket?

If \( 3 x+5 x+y=3 x+5 x+2 y \) then \( y=? \)