\(\text{This is just a point slope problem in disguise}\\ \text{the two points are }(x_1,y_1)= (1,5),~(x_2,y_2) = (-1,1)\\ \text{determine the slope of the line } a = \dfrac{y_2-y_1}{x_2-x_1}\\ \text{use that with either point to determine }b\\ \text{then }h(6) = a (6) + b\)