#### Answer

(a) $k = 47,000~N/m$
(b) $f = 1.8~Hz$

#### Work Step by Step

(a) Let's assume that the mass on each spring is 300 kg. We can find the spring constant for each spring.
$f = \frac{1}{2\pi}~\sqrt{\frac{k}{m}}$
$k = f^2~(2\pi)^2~m$
$k = (2.0~Hz)^2~(2\pi)^2~(300~kg)$
$k = 47,000~N/m$
(b) Let's assume that the mass on each spring is 370 kg. We can find the oscillation frequency.
$f = \frac{1}{2\pi}~\sqrt{\frac{k}{m}}$
$f = \frac{1}{2\pi}~\sqrt{\frac{47,000~N/m}{370~kg}}$
$f = 1.8~Hz$