please answer all as they are straight to the point, i will rate but i need them asap

The marginal costs of a defender for each of the final four years of service are $1.300,S1,500 52 100 and $2,700, respectively. If the challenger's minimum EUAC is 51,749, the defender should be replaced at the end of what year? (Note: Choose to recommending to replace immediately) A 3 B1 OG 4 OD 0 OE 2 An equipment bought four years ago for $4.490 has a current market value of $2,110. If kept for one more year, it will cost $1.430 in operation and maintenance costs and will have a market value of $1.680 at the end of the year. In conducting a replacement analysis for the equipment, which of those cash flows can be considered a surkoost? A. $4,490 B 51.430 OG $1,680 OD. $2,110