how to replace 1 element in matrix

I have matrix A and its a 4 by 5 I want to replace the element (3,4) and create a new matrix for it and name it B what would I do? D = A(3,4)=75 is what I have input but theres an error with to may = signs

Answer 1

[KSSV]

D = A(3,4)   % thats it 

Please don't ask very simple and basic questions in the community. Take a tutorial on basics of MATLAB.

[Brendan Steele]

Ive looked it up several times and there isnt a question where I can find an answer that works. If you know where I could find the basic rules that'd be great. I am taking a class and this is an issue I am having so please only respond with an answer.

[KSSV]

https://in.mathworks.com/help/matlab/learn_matlab/array-indexing.html

You can take a bsic turotials on this link:

https://in.mathworks.com/learn/tutorials/matlab-onramp.html?requestedDomain=