31. Dorothy buys her groceries online. The total cost that Dorothy pays is the sum of the
cost of her groceries and a flat-rate shipping fee of $6.1. Which equation shows the
correct relationship between the cost of Dorothy's online grocery purchases and the
total cost, including shipping?
A. R = X + 6.1, where X represents total cost ($) and R represents groceries ($).
B. R = 6.1X, where R represents total cost ($) and X represents groceries ($).
C. X = R - 6.1, where R represents total cost ($) and X represents groceries (5).
D. R = x + 6.1, where R represents total cost ($) and X represents groceries ($).