So there are 18 coins in total right?(4 quarters+3dimes+5nickels+6 pennies)
So the number of pennies is 6
So probability of pennies (6) out of the whole coins(18) is 6/18 right?
This can be simplified to 2/6(since the highest common factor is 3 and dividing both by 3 gives you 2 and 6)
So probability of a pennie out of the piggy bank is 2/6
6a
So you would write the factored equation as 6a(b+2)