Answer:
To find out how much money Dee had left after her purchases, we can use the equation: $120 - $55 - (3 × $18) = M. This equation represents the initial amount of money Dee had ($120) minus the amount she spent at the grocery store ($55) minus the cost of the three potted flowers ($18 each, so 3 × $18). By simplifying this equation, we can find the value of M, which represents the money Dee had left.