The formula of the Simple Interest is:
I=PRT
P for Principle Amount ($1200)
R for Rate (5%=

= 0.05)
T for Time in years (4 years)
I = 1200 × 0.05 × 4
= $240
Add the interest to the principle amount to check the balance
$1200 + $240 = $1440
Answer: A
(He has the side lengths in the wrong place in the cosine ratio)
Slope intercept form is y=mx+b where m is the slope and b is the y part of an intercept where x is 0. So the equation for slope (y1-y2)/(x1-x2) with y1 and y2 the y values of 2 points and x1 and x2 those points' x values, so if you would use the points (-2,0) and (0,5) (I used intercepts because they are easier, but you can use any points on the line) you would get (0-5)/(-2-0) and then 5/2 for the slope. plugging in then you get y=5/2*x+5