The dimensions of ab  in the equation p=a−t2bx  where p is pressure, x  is distance and t is time are

p=a−t2bx       ⇒            pbx=a−t2 ⇒                  [pbx]=[a]=[T2] Or [b]=[T2][p][x]=[T2][ML−1T−2][L]=[M−1T4] ∴          [ab]=[T2][M−1T4]=[MT−2]