Solution: According to the problem, (m-2) x 3 = 0, (2n+ 1) x 2 = 0. So: (m-2)=0, (2n+ 1)=0. Solution: m=2, n=-( 1/2). Substitute m=2 and n=-( 1/2) into MX 4-3x+n = 2x 4-3x-( 1/2). Then substitute x=- 1 into 2x4-3x-(1/2) = 2 * [(-1) 4]-3 * (1)-(1/2) = 9/2. ..... See clearly?