If the first year the stock is worth $200 per share and every year the value of the share will increase by $15, then, the equation that model the situation is:
y = 200 + 15m
Where m is the number of years that have passed and y is the value of the share.
So, the variable is m, the coefficient is the number beside m and it is 15, the operation is the sum and the constant is 200.