How would I write a "greater-than" expression into a linear equation?

Question

Like, y = 0x + 64.99, unless x >100 in which case its y=02.5x + 64.99

Answer 1

y = 64.99 if x< 100

y = 2.5x +64.99 if x > 100

for x < 100, the graph is a flat horizontal line

then it is a upward sloping straight line with slope = 2.5

the two lines are discontinuous, with a jump in y from 64.99 to 314.99

the point (100, 64.99) should be a darkened small circular dot.

the point (100, 314.99) should be an open small circular dot to indicate the graph does not include that point.