I am working on an LP problem where I have to model a constraint as:
"The total number of units of product A and B should be shipped in multiples of $1200$"
e.g. $700\text{(product A)} + 500\text{(product B)} = 1200\times1 = 1200$ or
$1800\text{(product A)} + 600\text{(product B)} = 1200\times2 = 2400$ or
$2000\text{(product A)} + 1600\text{(product B)} = 1200\times3 = 3600$
like that maximum shipment should be $6000$ units $(1200\times5)$, or I can say in other words as I can only ship $5$ batches of $1200$ units each.
Can somebody please help me to write such a constraint in algebraic form: $Xa + Xb = $?