Answer
a) 4z
b) 3$z^{2}$
c) -4z
d) 3$z^{2}$
Work Step by Step
$a$) z+3z = z(1) + z(3) = z(1+3) = 4z .....(Taking z out as common)
$b$) z$\cdot$3z = 3(z$\cdot$z) = $3z^{2}$
$c$) -z-3z = z(-1) - z(3) = z(-1-3) = z(-4) = -4z ......(Taking z out as common)
$d$) (-z)(-3z) = z(-1)$\cdot$3z(-1) = (-1)(-1)(z)(3z) = $1(3z^{2}$) = $3z^{2}$ ....(Since (-1)(-1)=1)
