the GCF is 7 which will give you 7(4n+6n)
explanation: 7 goes into 28 times and 7 goes into 42 6 times. and
To determine if a number is divisible by 7, take the last digit off the number, double it and subtract the doubled number from the remaining number. If the result is evenly divisible by 7 (e.g. 14, 7, 0, -7, etc.), then the number is divisible by seven.