Let: $r2=$ regular production quantity for period $2,02=$ overtime production quantity in period $2,$ i$1=$ inventory quantity in period $1,$ i$2=$ inventory quantity in period $2,$ and d$2=$ demand quantity in period $2.$ Correct formulation of the demand constraint for period $2$ is:

$r2+o2+i2-i1d2$

$r2+o2+i1-i2d2$

$r2+o2+i1-i2=d2$

$r2+o2+i2-i1=d2$