Question

A 20-kg box lays flat on the surface and has a string attached to its opposite sides (string A and B). String A is attached to another 20-kg box with on an inclined surface at 50 degrees. String B on the other hand is attached to a 5-kg box suspended in the air.

Answer 1

$$(m_1+m_2+m_3)a=m_2g\sin{50}-m_3g\\=(m_2\sin{50}-m_3)g\\ (20+20+5)a=(20\sin{50}-5)9.8\\ a=2.2\frac{m}{s^2}$$