The slsope of the graph of the line = 4.8 - 3 / 6-3 = 0.6
so we can write the equation as
c = 0.6d + b where b is some constant
When d = 3 c = 3 so we have
3 = 0.6* 3 + b
giving b = 3 - 1.8 = 1.2
Therefore the required linear equation is
c = 0.6d + 1.2
