(4) $21 q-7 p$ and $(3 q-p)(7)$

Step 1 ：The problem provides two expressions: \(21 q-7 p\) and \((3 q-p)(7)\).

Step 2 ：The first expression, \(21 q-7 p\), is already in its simplest form.

Step 3 ：The second expression, \((3 q-p)(7)\), can be simplified by distributing the 7 to both terms inside the parentheses.

Step 4 ：After simplification, both expressions become \(-7p + 21q\).

Step 5 ：So, the simplified forms of the expressions \(21 q-7 p\) and \((3 q-p)(7)\) are both \(\boxed{-7p + 21q}\).