If it's not what You are looking for type in the equation solver your own equation and let us solve it.
a in (-oo:+oo)
a-7 = -13 // + 13
a-7+13 = 0
a+6 = 0 // - 6
a = -6
a = -6
| -t+10=117/11 | | 5x-3/8=-3/8 | | 2x^2-20x+0=0 | | 6/7-1/5x=37/35 | | 2w+4/9=130/9 | | 2/7t-2/7=-5/21 | | 2a+4/7=-66/7 | | 5+1/3k=46/9 | | 4+6/7d=16/7 | | 5a-1/7=339/77 | | 4x-1=21/11 | | 8+5/7t=11/7 | | -5/7w+1=83/63 | | 7-2/5n=67/10 | | 5a+1/3=11/3 | | 4b-5/8=-5/8 | | 7-2/3t=17/3 | | 7t+5=65/6 | | -7k+6/7=-92/7 | | 2k+2/5=-68/5 | | 10-5w=50/7 | | 1/6n+9=145/16 | | 1-6w=-7/2 | | 3d-3=0 | | -6x-6=-42 | | 1/2n+3/8=45/88 | | 7k+2/3=170/3 | | =y(2y-11)+15 | | -5t+3=83/11 | | 5n+1/3=49/12 | | -7t+9=16 | | 7x+2=-29/10 |