In an equation, the different values show a specific mathematical relationship, and the equality represented by the symbol (=) is used to find an unknown value. In the case presented, the unknown value is the number of months Elizabeth can pay using her $300 gift certificate. This means the letter x in the equation represents the number of months.
Moreover, this x should be multiplied by the month membership or $15 considering Elizabeth will need to pay this fee each month and this should be added to the one-time fee of $50. This implies the first part of the equation is 15x + 50. Finally, this value should be equal to the total money in the certificate or 300. According to this, the equation is 15x + 50 = 300.
