Hi there!
All you need to do to solve for a is add 1.6 to both sides of the equation.
It will look like this:
a - 1.6 + 1.6 = -3.7 + 1.6
After this you will see that a = -2.1.
Hope this helps!
When in doubt just replace a with -2.1 and see if you still get -3.7. :)
