Shawna's work is shown below:

1. a2+72=252

2. a2+14=50

3. a2=36

4. a=6 m

In which step did Shawna make an error?

Step 1. She incorrectly applied the Pythagorean theorem.

Step 2. She incorrectly squared the numbers.

Step 3. She incorrectly isolated a2

Step 4. She incorrectly solved for a.