To determine the total number of plates shipped, we can set up the equation based on the information provided.
Given that 20% of the plates arrived broken and it is stated that 145 plates arrived broken, we can denote the total number of plates shipped as \( x \). Therefore, we can represent the relationship as follows:
\[ 0.20x = 145 \]
To find \( x \), we can divide both sides of the equation by 0.20:
\[ x = \frac{145}{0.20} \]
Calculating this gives:
\[ x = 725 \]
Thus, the total number of plates shipped is:
\[ \boxed{725} \]