If it's not what You are looking for type in the equation solver your own equation and let us solve it.
t in (-oo:+oo)
2*t+9 = 21 // - 21
2*t-21+9 = 0
2*t-12 = 0 // + 12
2*t = 12 // : 2
t = 12/2
t = 6
t = 6
| -10-3d=-25 | | 2b+9=-13 | | -7t+8=92 | | 4-4d=28 | | 3m+2=38 | | 5a=2a-12 | | 7p+9q=15 | | 2a+7=-9 | | -5+4d=35 | | -7k+2=-12 | | -7k+4=11 | | -6w+7=37 | | -1+3b=20 | | 7+2n=5 | | 7b-6=-27 | | -4d+9=-27 | | 6+4m=-26 | | 5+4n=21 | | -7+2a=11 | | 2d-8=-12 | | 6b+8=32 | | 6t+8=56 | | 3m+8=17 | | 7-5t=7 | | 4+4a=28 | | 9+5k=-46 | | 2w-1=15 | | 6b+2=44 | | 7n+6=27 | | 2t+2=18 | | 10+7d=45 | | -3w+1=-26 |