Answer: y = 4x + 1, 25 inches at 6 years old
Explanation:
Our y-intercept will be 1 (5 inches at a year old - 4 inches per year = 1) with a slope of 4 (4 inches a year). Our equation will look like this:
y = 4x + 1
Next, to solve for the length of the tusk at 6 years old, we will input this value of 6 and solve.
y = 4x + 1 = 4(6) + 1 = 25 inches
See attached for a graph.
We can also check our work using a different method.
6 years - 1 year = 5 years
5 years * 4 inches a year = 20 inches
20 inches + current 5 inches = 25 inches at 6 years