For Problems $2\mathrm{.}6$ and $2\mathrm{.}7,$ calculate the uniform load $($in addition to the beam weight$)$ that will cause the sections to begin to crack if they are used for $28-$ft simple spans. $f_c^{\text{'}}=4000,f_r=7\mathrm{.}5\sqrt[\phantom{2}]{f_c^{\text{'}}},$ normal$-$weight concrete, $=1\mathrm{.}0,$ and reinforced concrete weight $=150l\frac{b}{f}{t}^3.$

Problem $2\mathrm{.}6$