To find the cost of each mechanical pencil, let’s denote the cost of each mechanical pencil as \( x \).
Since mechanical pencils and erasers come in bundles of 10, if we assume Mr. Spears is buying 10 mechanical pencils, then the total cost for the mechanical pencils would be \( 10x \) (where \( x \) is the cost of one pencil).
The cost of the erasers for 10 erasers would be:
\[ 10 \times 0.50 = 5 \]
Now we can set up the equation for Mr. Spears' total expenditure:
\[ 10x + 5 = 25 \]
To match it with the original form you provided, we can express it as:
\[ 10(x + 0.50) = 25 \]
Thus, it should be:
10 (x + 0.50) = 25
The missing place in the equation is 10.