The $y$-intercept is the point at which the graph intersects the
$y$-axis. The graph will intersect the $y$-axis when $x = 0$.

Substitute 0 for $x$ in the expression.
$y = 6 + (−3)(0)$

$y = 6$

The slope is the value that y increases or decreases when $x$ increases by one.

Create a table of values or sketch the graph on graph paper.

You should notice that from $x = 0$ to $x = 1$ the $y$-value decreases by $3$. What is the slope?