#### Answer

a) $(2, 4)$ is not a solution of both equations, so it is not a solution of the system.
b) $(5, 30)$ is a solution of both equations, it is a solution of the system.

#### Work Step by Step

a) $(2, 4)$
$x + y = 8$
$2 + 4 = 8$
$6\ne8$ False
$3x+2y=21$
$3(2)+2(4)=21$
$6+8=21$
$14\ne21$ False
b) (5, 3)
$x+y=8$
$5+3=8$
$8=8$ True
$3x+2y=21$
$3(5)+2(3)=21$
$15+6=21$
$21=21$ True