Answer
$(a)$ $(-3,7)$
$(b)$ $(-a,b)$
$(c)$ $(4, -1)$
$(d)$
$A(3, 3)$ => $A'(-3, 3)$
$B(6, 1)$ => $B'(-6, 1)$
$C(1, -4)$ => $C'(-1, -4)$
Work Step by Step
The reflection about $y$-axis is to change $x$ value sign of a point and keep the $y$ value the same. It means that:
$A(x, y)$ => $A'(-x, y)$
$(a)$ The point $(3, 7)$ => $(-3, 7)$
$(b)$ The point $(a, b)$ => $(-a, b)$
$(c)$ We do the same to find the point vice versa.
$(-4, -1)$ was $(4, -1)$
$(d)$ We have to apply the same idea here, on each of these points:
$A(3, 3)$ => $A'(-3, 3)$
$B(6, 1)$ => $B'(-6, 1)$
$C(1, -4)$ => $C'(-1, -4)$
