This a linear function y = mx + b , where m = slope (rate of change), then:
y = (1/3).x + b. Now we have to calculate b. We know tat f(3) = 5, that means if we replace x by 3 , then y = 5:
5 = (1/3)(3) + b→ 5 = 1 + b and b = 5-1 = 4, then the final equation is
y = (1/3).x + 4