If t varies as v, and t = 2 4/7 when v = 13/14, find v when t = 2 1/4 ... v=. Direct variation ...

if t varies as v, then t = Kv (where K is the constant of proportionality)

when t = 18/7, v = 13/14

then 18/7 = 13K/14 (i substituted with the values of v and t to find K)

36 = 13K - - - > K = 13/36 - - - > t = 13v/36

when t = 9/4:

9/4 = 13v/36 (i substituted with the value of t to find the value of v)

81 = 13v - - - > v = 81/13 = 6 3/13