Here is the prediction equation formula to find the prediction equation on your own. As per the formula, adding the intercept point of the regression line and the y-axis with the multiplied value of first data set and the slope of the regression line will give you the result. Also, this page shows you the formulas for calculating the slope and intercept. First, draw a line of fit for the data given and write its equation in slope-intercept form then use the equation to predict the number.
x and y are the variables.
m = The slope of the regression line
a = The intercept point of the regression line and the y axis.
N = Number of values or elements
X = First Data Set
Y = Second Data Set
∑XY = Sum of the Product of First and Second Data Set
∑Xm = Mean of First (X) Data Set
∑Ym = Sum of Second (Y) Data Set
∑X2 = Sum of Square of First (X) Data Set Values
x = Number of duration/Valdity
Just submit the input values in the prediction equation formula and do the demanding operations to get the result. Also, you can make use of the related calculator to make your calculations easier and quicker.
Calculator 
Formula 
