$\clubsuit\cdot \clubsuit=9$

$\clubsuit=3$

$\clubsuit+\heartsuit=13$

$\heartsuit=13-3$

$\heartsuit=10$

$\diamondsuit\cdot \clubsuit+\heartsuit=28$

$\diamondsuit=(28-10):3$

$\diamondsuit=6$

$\clubsuit\cdot \heartsuit-\diamondsuit=$$3\cdot 10-6$

$\clubsuit\cdot \heartsuit-\diamondsuit=24$