Aduck's mass at birth was 0.05 kilogram. the duck gained approximately 0.042 kilogram each week. after how many weeks is the duck's mass 0.890 kilogram?

Given that the first mass of the duck is 0.05 kg and it gains weight at a rate of 0.042 kg/week, the equation that would represent this scenario is,
                               y = 0.05 + 0.042x
where y is weight and x is the number of weeks. To determine the number of weeks in which the duck's mass becomes 0.890,   
                            0.890 = 0.05 + 0.042x
The value of x from the equation is 20.