I would recommend "Introduction to Linear Algebra," by Gilbert Strang. It is a compact but very helpful textbook reference written by a well-known MIT professor. There is a corresponding online MIT course that is free, so that's a bonus. I am currently using it to study linear algebra with no class or previous experience, and I think it does a solid job of explaining things. Each section in the book has a set of questions for you to work through, and answers to selected questions appear in an appendix at the end of the book.
Hope this helps!
If you mean that you want to solve the equation for v, then all you need to do is to multiply both sides by 3:

It should be 75000. I don’t know. I looked this up but I still hope this helps!
Answer:
72 in^2
Step-by-step explanation:
The area of the square in the middle is
A = s^2 = 6^2 = 36
The area of the triangle on the left is
A =1/2 bh = 1/2 ( 6*6) = 18
The area of the triangle on the right
A = 1/2 bh = 1/2(6*6) = 18
Add the areas together
36+18+18 = 72