The equation of the line:
y = m x + c
m is the slope , c is constant
so m = 1/2 (given)
so y = (1/2) x + c
c will be calculated from the given point as y -1 when x =-3
then -1 = (1/2) * -3 + c
c = -1 +(1/2)*3 = 1/2
so y = (1/2) x + (1/2)
the graph of function is as shown in the figure