HELP ASAP IN 24 HRS! btw is there a formula

Question

Jenny started saving money on Monday.

Each day, she saved $0.40 more than the amount saved the day before. If she saved an average of $2.40 from Monday to Friday, find the amount she saved on Monday.

Answer 1

(x+ x+.4 + x+.8 + x+ 1.2 + x + 1.6)/5 = 2.4

5x + 4 = 12

5x = 8

x = 8/5=1.6

x = $1.60 on Monday

$2 on Tuesday

$2.40 on Wednesday

$2.80 on Thursday

$3.20 on Friday

total = $12 for 5 days

average for the week = $12/5 = $2.40 per day