$3.$ In a multiple$-$effect evaporator, the steam economy is $3.$ If $1000$ kg$/$hr of steam is supplied to the first effect, how much vapor is produced?

$-$ a$)1000$ kg$/$hr

$-$ b$)2000$ kg$/$hr

$-$ c$)3000$ kg$/$hr

$-$ d$)4000$ kg$/$hr