So that means its--> 15cos(3t)/-12sin(4t)Do you know that dy/dx = (dy/dt)/(dx/dt)? This is a version of the chain rule.
Yes, but write that more carefully, with parentheses, (15cos(3t))/(-12sin(4t)), and simplify it a bit (canceling a common factor). There's not much more you can do.So that means its--> 15cos(3t)/-12sin(4t)