Final answer:
The equation of the straight line is y = 3x - 8. The coordinates of the point of intersection with the line y = x are (4,4).
Step-by-step explanation:
The equation of a straight line can be expressed in the form y = mx + b, where m is the gradient and b is the y-intercept. Given that the line passes through the point (3,1) and has a gradient of 3, we can substitute those values into the equation to find the value of b. Thus, the equation of the line is y = 3x - 8.
To find the coordinates of the point of intersection with the line y = x, we can set the two equations equal to each other and solve for x. This gives us the equation x = 3x - 8. Solving this equation, we find that x = 4. Substituting this value of x into either equation, we find that y = 4. Therefore, the coordinates of the point of intersection are (4,4).