You have an even probability of getting a red card or a black card. This is true because there are an even number of red cards and black cards. (25 or 26 of each, depending on if you include jokers.) Therefore, there is an even probability of getting a red card or a black card. It has to be 50%, because that is the only number in which two options can have equal numbers.
The gradient is the x-coefficient. The y-intercept is the constant. These are listed in the table in the first attachment. The graphs are shown in the second attachment.
