Session Timed RTI Scheduler Course Catalog HS Course Cate$-$calculus$-$ab$/$test$/$x$2$dd$7$feea:course$-$challenge Planning Google Classroom Chem APUSH AP Gov AP Lang $AP$ Cal $AB$ Khan Academy The shaded region is bounded by the graph of the function $f(x)=\sqrt[\phantom{2}]{x+3},$ the line $x=k,$ and the $x-$axis. If the region has area $18,$ what is the exact value of $k?$