Slope intercept form has the general form of y = mx + b, where m is the slope and b is the y-intercept.
You are given the y-intercept with the point (0, -10). Thus, the y-intercept is -10.
You are also given the slope of 1.
Next, just plug your numbers in!
y = 1x - 10
y = x - 10
Hope this helped!