A two-digit number is such that the product of its digit is 72. If the tens digit is subtracted from the number, we get 81. Represent the situation in quadratic form. 

Let the number be 10x + y where x represents the tens digit and y represents the units digit. 

Given that, xy = 72 

$\Rightarrow \mathrm{x}=\frac{72}{\mathrm{y}}$ ….(i) 

Also, 10x + y - x = 81 

$\Rightarrow$9x + y = 81 

Put value from (i).  

$9\left(\frac{72}{\mathrm{y}}\right)+\mathrm{y}=81$ 

$\Rightarrow {\mathrm{y}}^2-81\mathrm{y}+648=0$