Zina spends 1.5 hours setting up her sewing machine and making one hat. the total amount of time spent making hats can be represented by the sequence below. 1.5, 2.25, 3.0, 3.75, which recursive formula can be used to determine the total amount of time spent making hats based on the total amount of time spent previously?

Based on the sequence, it shows an Arithmetic Sequence. The difference from one number to the other is 0.75. In order to get the sum of the sequence at a given N items, you need to use the formula. 

The formula is S = N/2 [2a1 + (N-1)d].
S = sum
N = number of items
a1 = first item of the sequence
d = difference from one item to the next item