$\text{ABCD}$  is a rectangle with $AB=16units$  and $BC=12units$ . $\text{F}$  is a point on

$\text{AB}$  and $\text{E}$  is a point on $\text{CD}$  such that $\text{AFCE}$  is a rhombus. Then, $\text{EF}$  is

Area of rectangle $ABCD$ $=$ area of triangle $ABE$ $+$ area of rhombus$AFCE$ $+$  area of triangle $FDC$

$16\times 12=\left(\frac{1}{2}\times \frac{7}{2}\times 12\right)+\left(\frac{1}{2}\times 20\times EF\right)+\left(\frac{1}{2}\times \frac{7}{2}\times 12\right)$

                                                $\left(\because AC=20unitsandCF=\frac{25}{2}units\right)$

$\Rightarrow 192=21+10EF+21$

$\Rightarrow 192=42+10EF$

$\Rightarrow 10EF=150$

$\Rightarrow EF=15units$