Let $${1 \over {16}}$$, a and b be in G.P. and $${1 \over a}$$, $${1 \over b}$$, 6 be in A.P., where a, b > 0. Then 72(a + b) is equal to ___________.

Consider an arithmetic series and a geometric series having four initial terms from the set {11, 8, 21, 16, 26, 32, 4}. If the last terms of these series are the maximum possible four digit numbers, then the number of common terms in these two series is equal to ___________.

The total number of 4-digit numbers whose greatest common divisor with 18 is 3, is _________.

If the arithmetic mean and geometric mean of the p^th and q^th terms of the
sequence $$-$$16, 8, $$-$$4, 2, ...... satisfy the equation
4x² $$-$$ 9x + 5 = 0, then p + q is equal to __________.