In the first step, differentiate normally, but multiply the term with the y by dy/dx.
12x+(10y*dy/dx)-7=0
Next, you have to solve for dy/dx, so add 7 to both sides and subtract 12x from both sides
10y*dy/dx=7-12x
Divide both sides by 10y
Dy/dx= (-12x+7)/(10y)
And this should be your answer!
