To find the difference in the cost of gas from last week to this week, we can simply subtract the amount Bonnie spent last week from the amount she spent this week.
Cost last week: $32.78
Cost this week: $35.45
Difference = Cost this week - Cost last week
Difference = $35.45 - $32.78
Difference = $2.67
So, the difference in the cost from last week to this week is $2.67.