Answer
$a+c \lt b+d$
Work Step by Step
Consider the inequality $a \lt b$
This gives:
$a+c\lt b+c$ ....(1)
Also, we have $c \lt d \implies c+b \lt d+b$ ...(2)
Add the both equations (1) and (2).
This gives: $a+c\lt b+c \lt b+d$
Thus, $a+c \lt b+d$
