To find the total number of glass plates shipped, you can set up the equation based on the information given. Since 20% of the plates arrive broken, this means that 145 broken plates represent 20% of the total shipped plates.
Let \( x \) be the total number of plates shipped. According to the problem:
\[ 0.20x = 145 \]
To find \( x \), divide both sides of the equation by 0.20:
\[ x = \frac{145}{0.20} \]
Calculating this gives:
\[ x = 145 \div 0.20 = 145 \div \frac{1}{5} = 145 \times 5 = 725 \]
Therefore, the total number of plates shipped is 725 plates.