If it's not what You are looking for type in the equation solver your own equation and let us solve it.
-1a=21
We move all terms to the left:
-1a-(21)=0
We move all terms containing a to the left, all other terms to the right
-a=21
a=21/-1
a=-21
| 6=x+3x31 | | 25x2+15x=0 | | 3x-1/4=7 | | 9x+10÷4-4x-4÷10=14 | | 76=70t-16t2 | | 1/5x-9=0 | | 3v+4=9v-98 | | 2s+62=6s-62 | | 3a-28=a+12 | | 10p-17=5p+3 | | 4c-77=c+22 | | 6y+2y=730 | | 4b-63=b | | 2p-35=p | | 9s+96=7s+100 | | 95/10=x/1 | | 4u+7=9u-28 | | 7y+6=10y-6 | | 4x-8÷3=x-5 | | 0,7x=0 | | 100=v4+1/2(8)(4)^2 | | 11x-12=8x+9 | | 44+8y-15y=6 | | 0,6+(0,5y-1)=y+0,5 | | 2*x+1=1400 | | 8y-9=47 | | 15=2+2x-4 | | 2*x+1=1300 | | 0.2x+3+0.8x=0 | | 2x-11=x-17 | | 2x^2-110x+625=0 | | x+4=4x-12 |