Okay. The first function clearly says that "Hey, my y intercept = 5." You can see from the figure. |dw:1466064621138:dw| Sorry for the bad drawing, was trying to depict the function can be anything. For the second function. Lets say the no of months in summer is x. Lets say the total books he read is y. The function is then: $6x + 3 = y$ Assuming you know how to find y intercept in equation of line, the intercept is 3. If you dont know it, general eqn of line is $mx + c = y$ where m is always the slope of line and c is y intercept. Hence last function has y intercept equal to 4.