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This thing really frustrated you for a long time: Here is a simple solution to help you solve this and others:

Could be you are missing on a very simple step:

Explore this example carefully, see the mistake then replace the numbers with your own figures:

Two point charges lie on the x axis. A charge of + 6.5 µC is at the origin, and a charge of -1.5 µC is at x = 10.0 cm.

What is the net electric field at x = -2.0 cm?
I found the electrical field for each charge using the equation

E= k(q)/ r^2.

My calculations were:
For the first charge- (8.99e9)(6.5e-6)/(.2^2) = 1460875 and
(8.99e9)(1.5e-6)/(.2 + .1)^2 = 149833.33

For the second. I added the two
to determine the net field- 1610708.33N/C.

This answer was incorrect.
So then I used -1.5e-6, recalculated and got net of 1311041.67; also
incorrect.

Can anyone tell me if I am I using the wrong equation or
doing something else wrong?

You are doing something else wrong. The distance from charge 1 to
the point where the field is desired is 0.02 m, not 0.2. Likewise for
charge 2, it is 0.1 + 0.02m , not 0.1 + 0.2.