Since this line is parallel to y = 3x + 1 their slopes are equal. The slope is equal to 3. The line is also passing the point (-3,4).
This is the format of the line parallel to y = 3x + 1
y = 3x+ b
This line passes through point (-3, 4)
Replacing the values of y and x coming from the coordinates of (-3, 4)
4 = 3 * (-3) + b
Solving for the y-intercept b
4 = -9 + b
b = 4 + 9
b = 13
Knowing the slope as equal to 3 and the y-intercept as 13 the equation of the line is
y = 3x+13