Explanation:
(-a)⁴ / (-a)³ = -a
since both terms have the same exponent base (-a), we can simply do the regular exponent arithmetic (multiplication = +, division = -)
4 - 3 = 1
so, the exponent 1 remains.
it works also, if we process the exponents first
(-a)⁴ = a⁴
(-a)³ = -(a³)
a⁴/-(a³) = a/-1 = -a