$9\mathrm{.}2$ A pretensioned beam of rectangular section, $200$ mm wide and $450$ mm deep, is prestressed by $10$ wires of $5$ mm diameter located at an effective eccentricity of $150$ mm $.$ The maximum shear force at a particular section is $120$ kN $.$ If the modular ratio is $6,$ calculate the flexural bond stress developed assuming,

$($a$)$ the section as uncracked,

$($b$)$ the section as cracked.