Firstly we need to count how much is 15% from $40:
40 * 15% =
= 40 * 15/100 =
= 40 * 3/20 =
= 2 * 3/1 =
= 2 * 3 =
= 6 [dollars]
So the kit costed $40 - $6 = $34 after the first general discount. Now the question is if the coupon relates to the original price or to the lowered price. We'll do both:
If it relates to the original price, we need to find how much is 25% of $40. We can do it in mind - it's $10. So with two discounts the price would be $40 - $6 - $10 = $24.
However, if it relates to the lowered price, we need to find how much is 25% from $34:
34 * 25% =
= 34 * 25/100 =
= 34 * 1/4 =
= 8.5 [dollars]
So the final price in such a situation would be $40 - $6 - $8.5 = $25.5.
