Mathematics

Problem

If the radii of the circles

(x-1)^2 + (y-2)^2 = 1

and

(x-7)^2 + (y-10)^2 = 4

are increasing uniformly w.r.t. time as 0.3 unit/s and 0.4 unit/s respectively, then they will touch each other at

t

equals to a. 45 s b. 90 s c. 11 s d. 135 s