If by "taxi distance" you mean travelling along the sides of the right triangle created by the two points.
t=|x2-x1|+|y2-y1|
t=5+4
t=9 units
If you mean the actual distance between the two points then:
d^2=(x2-x1)^2+(y2-y1)^2
d^2=(7-2)^2+(9-5)^2
d^2=25+16
d^2=41
d=√41 units
d≈6.4 units (to nearest tenth of a unit)
