Based on the given information, if p is the number of pens, you can write the following equation:
p + 5 - (p + 5)/2 = 16
the first term is the total number of pen Shanice had on Monday, 5 term is the bought she did on Tuesday, and the third term means that the number of pen she lost on Wednesday was half of the pens she had before that day, that is (p + 5). Finally, the numper of pan she has is 16, the right side of the equation.
Then, with an equation you can represent the given situation.
To determine the number of pens Shanice had on Monday, solve the equation as follow:
p + 5 - (p + 5)/2 = 16 apply distribution property left side
p + 5 - p/2 - 5/2 = 16 multiply by 2 both sides
2p + 10 - p - 5 = 32 simplify like terms left side
2p - p + 10 - 5 = 32
p + 5 = 32 subtract 5 both sides
p = 32 - 5
p = 27
Hence, Shanice had 27 pens on Monday.