Question 200524
Given {{{S = Kwd^3}}}; where K is some constant. First thing we need to do is get enough info to solve for K. Lucky for you, the problem provides that.
{{{90 = K*2*3^3}}}
{{{90 = K * 54}}}
{{{90/54 = K}}} So we know K now
{{{S =(90wd^3)/54}}} Put K in the original equation

Now solve when w=5 and d=2
{{{S =(90wd^3)/54}}}
{{{S =(90*5*2^3)/54}}}
{{{S = (90*5*8)/54}}}
{{{S = 66.667}}}