Looks like you would like to solve for y.
Remember that we would like to isolate y by performing the same operations on both sides of the equation until y remains on one side by itself.
To start add 1.2 to both sides.
-7.8 + 1.2 = y/2.45 - 1.2 + 1.2.
This lets us simplify to
-6.6 = y/2.45.
Now multiply both sides by 2.45.
-6.6*2.45 = y/2.45*2.45.
Now we have
-16.17 = y.
So these operations isolated y, and we can now read the solution, y = -16.17.
Hope that helped.