hi! I need help with this one, in MATLAB CODE, 3D matrix

Hi! I need to do the following, but I don't know how to manipulate the picture! The picture is uploaded in this link: https://drive.google.com/file/d/0B--rsLtWyjqNeFFfeGVPeW5YWFU/view?usp=sharing

I already have a code but, I dont know how to manipulate 3d matrix

Instructions:

Use google maps / earth to capture an image like the one shown. Write a program in Matlab that upload the image and estimate the area (land) of Puerto Rico from the satellite photo.

Suggested procedure:

1. Generate an array that contains only the scale of the image (upper left corner). Manipulate this array to identify the equivalent area of a pixel
2. Generate an arrangement that contains only Puerto Rico. Manipulate this arrangement to "separate the land from the sea." Determine the number of pixels representing land and obtain your estimate of the area of Puerto Rico using the equivalent area per pixel found in point 1.

%My program:

addpath('C:\Users\Anthony\Desktop\UPRM\Segundo año\Primer semestre\Inge3016\Asignaciones\Asignación #5');
Z = imread('PuertoRico.jpg');

Zrojos  = Z(:,:,1);
Zverdes = Z(:,:,2);
Zazules = Z(:,:,3);

figure; 
subplot(221); image(Z); axis image; title('original')
subplot(222); image(Zrojos); axis image; colormap(gray); title('rojos')
subplot(223); image(Zverdes); axis image; colormap(gray); title('verdes')
subplot(224); image(Zazules); axis image; colormap(gray); title('azules')

figure;
plot(image(OV));

Please Help me! Thanks a lot!