Hi:) is there a reason why the gradient of vertical lines are undefined?

What is the length of the missing leg in this right triangle? 18 mm 24 mm 26 mm 32 mm

Adam plans to choose a video game from the section of the store where everything is 75% off. he writes the expression d-0.75d to find the sale price of the game if the original price is d dollars. gena correctly writes another expression, 0.25d, that will also find the sale price of the game if the original price is d dollars. use the drop down menus to explain each part of adams and rena's expression

What is the slope of the equation y =