Question 168319
{{{a=k(d[1])(d[2])}}}  find the constant k 
:
{{{30=k(10)(6)}}}
{{{30=60k}}}
{{{k=1/2}}}
:
now plug in next set of diagonals using the found value of k to find the area desired
:
{{{a=(1/2)(8)(13)}}}
{{{highlight(a=52)}}}sq inches