It must be a degree 3 polynomial with integer coefficients with zeros -8i and 7/5
if -8i is a zero, then +8i (it's conjugate) must also be a solution. So, tnis gives you
(x-8i)(x+8i)(x -7/5) multiply the first 2 factors
(x2-64i2)(x-7/5) =(x2 + 64)(x - 7/5), but you need integer coefficients, so, change x - 7/5 to 5x - 7
this gives yoiu (x2 + 64)(5x - 7). Multiply these together, and you have
5x3-7x2 + 320 x -448 this is your 3rd degree polynomial