Let \( x \) be the total number of plates shipped. According to the information provided, 20% of the plates arrived broken. Therefore, we can express the number of broken plates mathematically as:
\[ 0.2x = 145 \]
To find the total number of plates shipped, we can solve for \( x \):
\[ x = \frac{145}{0.2} \]
Calculating that gives:
\[ x = 145 \div 0.2 = 145 \times 5 = 725 \]
Thus, the total number of plates shipped is 725 plates.