For Nos $39$ to $41$: A rectangular foundation $3m6m$ as shown in the plan transmits a stress of $150$ kPa on the surface of a soli deposit?

Determine:

$39.$ the increase in vertical stress under point $A$ at a depth of $3$ m below the ground surface is nearest to

a$.)120\mathrm{.}25$ kPa

b$.)88\mathrm{.}75$ kPa

a$)96\mathrm{.}2$ kPa

d$.)72\mathrm{.}15$ kPa

$40.$ the increase in vertical stress under point $B$ at a depth of $6$ m below the ground surface is nearest to

a$.)24\mathrm{.}04$ kPa

b$.)18\mathrm{.}03$ kPa

c$.)30\mathrm{.}05$ kPa

d$.)102\mathrm{.}15$ kPa

$41.$ the increase in vertical stress under point $C$ at a depth of $2$ m below the ground surface is nearest to

a$.)30\mathrm{.}35$ kPa

b$.)15\mathrm{.}85$ kPa

c$.)9\mathrm{.}51$ kPa

d$.)12\mathrm{.}68$ kPa