$4-6$ Select the lightest W$6$ section that will resist a service tensile load, $P_D=50k$ and

$P_L=70k.$ The member is to be $20$ ft long and is assumed to have two lines of holes

in each flange and one line of holes in the web. Assume there are four bolts in each

line $3$ in on center. All holes are for $7/8-$in $\frac{O}{?}$ bolts. Use A$992-$Grade $50$ steel.