$2/$ given the following property, If

m$<$ or $=$ f$($x$)<$ or $=$ M for a$<$ or $=$ x $<$ and $=$ b$,$ then m$($b$-$a$)<$ or $=($a down and b up$)$ f$($x$)$dx$<$ or $=$ M$($b$-$a$),$ estimate the value of the integral $(3$ up and $1$ down$)[$square root $($x$^2+3)$ dx$]$