Look at what we're asked to find: 2a+3b−3c.
Notice that 3b−3c=3(b−c). Now glance at the given equations:
a−6b+6c=4⟹a−6(b−c)=4⋯(1)
6a+3b−3c=50⟹6a+3(b−c)=50⋯(2)
See how b and c always appear together as (b−c)? That means we don't need to find b and c individually — we only need (b−c) and a.
From Equation (1):
a=4+6(b−c)⋯(3)
Substitute into Equation (2):
6[4+6(b−c)]+3(b−c)=50
24+36(b−c)+3(b−c)=50
39(b−c)=26
b−c=3926=32
Plug b−c=32 back into Equation (3):
a=4+6×32=4+4=8
2a+3b−3c=2a+3(b−c)
=2(8)+3(32)
=16+2
=18