Straight line:
y = mx + c
m is the slope of the graph and c is the y-intercept
In this case, m = 5 as stated in the question, so...
y = 5x + c
By substituting the given co-ordinates (-2,-1) into this equation, we can find c
-1 = 5(-2) + c
-1 = -10 + c
-1 + 10 = -10 + c + 10 (Add 10 to both sides)
9 = c
c = 9
Put c = 9 into the equation:
y = 5x + 9
To find AB(x) and BC(y), you can do(there are multiple ways you can do this):
tan A = 
tan 60° =
or (tan 60°) · 7 = y
tan 60° = 
√3 · 7 = y
7√3 cm = y
sin B = 
sin 30° =
or 
sin 30° =
= 
x = 
x = 14 cm
AB = 14cm
BC = 7√3 cm