If log₇ 5 = a, log₅ 3 = b and log₃ 2 = c, then the logarithm of the number 70 to the base 225 is

If $${\log _5}{{(a + b)} \over 3} = {{{{\log }_5}a + {{\log }_5}b} \over 2}$$, then $${{{a^4} + {b^4}} \over {{a^2}{b^2}}}$$ is equal to