Load up and show MATLAB$$s image $$coins$.$png$($Figure $3\mathrm{.}4($a$))$ using the following line:

z $=$ imread$($coins$.$png$)$; figure, imshow$($z$)$

This will enter a matrix z in MATLAB$$s memory. Values close to $0$ correspond to dark, and values

close to $255,$ to light pixels. Propose and implement a simple way to replace the background of

the image with white, similar to the image shown in Figure $3\mathrm{.}4($b$).$