1.8ax+8a 2.m⁶+m⁷ 3.18y⁵+12y⁴ 4.36mn⁵+63m²n⁶

To simplify the expressions you've provided, let's break each one down step by step.

1. Expression: \( 1.8ax + 8a \)
   We can factor out the common term \( a \):
   \[ a(1.8x + 8) \]

2. Expression: \( m^6 + m^7 \)
   We can factor out the common term \( m^6 \):
   \[ m^6(1 + m) \]

3. Expression: \( 18y^5 + 12y^4 \)
   First, find the GCD of the coefficients \( 18 \) and \( 12 \), which is \( 6 \), and then factor out \( 6y^4 \):
   \[ 6y^4(3y + 2) \]

4. Expression: \( 36mn^5 + 63m^2n^6 \)
   The GCD of the coefficients \( 36 \) and \( 63 \) is \( 9 \), and the common variable factors are \( m \) (the lowest power is \( 1 \)) and \( n^5 \) (the lowest power is \( 5 \)). So, we factor out \( 9mn^5 \):
   \[ 9mn^5(4 + 7m) \]

In summary, the simplified forms are:

1. \( a(1.8x + 8) \)
2. \( m^6(1 + m) \)
3. \( 6y^4(3y + 2) \)
4. \( 9mn^5(4 + 7m) \)