If it's not what You are looking for type in the equation solver your own equation and let us solve it.
m in (-oo:+oo)
4*m+7 = -21 // + 21
4*m+7+21 = 0
4*m+28 = 0 // - 28
4*m = -28 // : 4
m = -28/4
m = -7
m = -7
| -6w-8=-44 | | 10+6m=22 | | -2w-8=-20 | | 6b+9=-63 | | -7m+7=-56 | | 6-2k=-10 | | 4p-5=11 | | 4-2d=22 | | -3d-8=-32 | | 6-4n=10 | | 10+5m=45 | | 9+7d=9 | | 2a+8=12 | | 7b-4=66 | | 5m-4=-4 | | 6d+10=-14 | | 6m+8=-34 | | 4k+8=28 | | -5t+8=-32 | | 10-5k=10 | | 3+4b=3 | | 5w+3=23 | | 10+5t=-30 | | -5w-8=32 | | -3t+5=-31 | | 5m-8=-68 | | 8+5d=23 | | -6m-2=-44 | | 37x+8=7 | | -3t+1=-8 | | 5k+3=-27 | | 9+5b=44 |