To find the total number of plates shipped, we can use the information given about the percentage of broken plates. We know that 20% of the plates arrive broken, and in the last shipment, 145 plates arrived broken.
Let \( x \) be the total number of plates shipped. According to the information given:
\[ 20% \text{ of } x = 145 \]
We can express this in equation form:
\[ 0.20x = 145 \]
To find \( x \), divide both sides of the equation by 0.20:
\[ x = \frac{145}{0.20} \]
Calculating this gives:
\[ x = 145 \div 0.20 = 725 \]
Therefore, the total number of plates shipped is \( 725 \).
So, the answer is: 725 plates.