Signal conversion problem in Image Processing

How can I solve this question in matlab and how do we find the answer?

I tried this code blog:

r1= input('enter r1: ');

r2= input('enter r2:');

s1= input('enter s1:');

s2= input('enter s2:');

r=[0 r1 r2 255], [0 s1 s2 255];

if r < r1

s=r*(r1/s1);

elseif r1<r & r<r2

x=tan((r2-r1)/(s2-s1))

s(r-r1)*x

else

s=r*(r2/s2)

end

plot(s);

I would be glad if you help.