A basement is $12\mathrm{.}4$m wide and $15\mathrm{.}8$m deep. You are designing the floor frame over a third of this basement. You are

placing two built$-$up wood beams on the rear wall and the bearing wall to support joists, equally dividing the width of

the space. Assume that the clear spans as $12$m and $5\mathrm{.}4$m and that this floor is topped with a $50$mm thick concreteFind the smallest joist between beams if you were to use Grade $1$ Douglas F$-$L joists

@ $600$mm spacing and with bridging