Given the matrices p=(2/3 -1/4) and q=(5/-2 4/6) evaluate 3p+2q?

Perhaps you have p = [2, -1; 3, 4] where commas separate columns and semicolons separate rows. Then
  3p + 2q
  = 3[2, -1; 3, 4] + 2[5, 4; -2, 6]
  = [6, -3; 9, 12] + [10, 8; -4, 12]    (the multiplier is applied to every term)
  = [16, 5; 5, 24]    (corresponding terms are added)

In your format as we understand it, this would be
  (16/5 5/24)