Changes along a line

Y-change on a line ●○○○○ 10 ptsMoving along a particular line in the Cartesian plane, when the $x$ -value increases by 3 units, the $y$ -value increases by 7 units. When the $x$ -value increases by 9 units, by how many units will the $y$ -value increase?
Difference of a linear function ●○○○○ 10 ptsThe function $f$ is linear and satisfies $f(d+1)-f(d) = 3$ for all real numbers $d$ . What is $f(3)-f(5)$ ?
Positive difference from an average ●○○○○ 10 ptsThe average of the numbers 23 and $x$ is 27. What is the positive difference between 23 and $x$ ?
Widget output difference on two days ●●○○○ 20 ptsOn Monday, David produces $w$ widgets per hour and works for $t$ hours. On Tuesday, he works for $2$ fewer hours than on Monday, but produces $4$ additional widgets per hour. If $w = 2t$ , how many more widgets did David produce on Monday than on Tuesday?

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