1)  (m³n⁵)(mn⁴)
     -----------------
      m⁻³n²
Simplify.
m⁴n⁹
-------
m⁻³n²
When the bottom power is a negative, you add it to the power on top, & when the power is a positive, you subtract it.
m⁴ + m³ = m⁷
n⁹ - n² = n⁷
So, our answer for #1 is m⁷n⁷
2)  6a²b³
     ---------
        4a
Please read rules in #1.
6 / 4 = 3/2 & a² - a = a
So, our answer is 3a
                               -----
                                 2
3)  5⁶a⁶b³
     ---------
       5²ab³
5⁶ - 5² = 5⁴ AND a⁶ - a = a⁵ AND b³-b³ = 0
So, our answer is 5⁴a⁵
Simplify 5⁴
5 × 5 × 5 × 5 = 625
So, our final answer is :
625a⁵
~Hope I helped!~