Solve the following system of equations for $z$ and for $y$ :

System of Equations:

Value of $z$

Value of $y$

$y=9+3z$

$y=49-5z$

Solve the following system of equations for a and for $b$ :

System of Equations:

Value of $a$

Value of $b$

$4a+2b=20$

$15a+5b=60$