Question 591299
Let x = months, y = length


Equation is: y = 3x + 290


You get this by adding the initial length of 290 cm to the variable length 3x cm. For example, in month zero (the start), the length is y = 3(0)+290 = 290 and in one month, the length is y = 3(1) + 290 = 293



From here, plug in y = 470 and solve for x:



y = 3x + 290


470 = 3x + 290


470-290 = 3x


180 = 3x


180/3 = x


60 = x


x = 60


So in 60 months, or 60/12 = <font color="red">5 years</font>, the whale will be 470 cm long