What is the taxi distance between a(2, 5) and b(7, 9)?

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)