ElectricPavlov

2x(x+78)(x+38)8x      Lets expand the two portions in the parentheses first

2x(8x) ( x^2 +38x +78x + 2964)       and simplify a bit   (2x * 8x = 16x^2)

16x^2 (x^2 + 116x + 2964)                and use distributive property to finish (if you want to go farther)

16x^4 + 1856x^3 + 47424x^2

I see what you are saying .....   Your answer calc is correct but it  needs to state the temperature increase was .018495 DEGREES per year NOT 1.85 %.

  Another way      say the ave temp was 100 degrees   then fifty years late the temp was 102.5    the average temperature increase over the 50 years was   .018495 dgrees per year not 1.85%      Do you see?   Thanx !

287 l of 57%  = 163.59 l of pure fertilizer

x = amount of 20%       .20 x

287-x = amount of 61%  =  (287-x)(.61)

.20x + (287-x)(.61) = 287(.57)

.20x +175.07 - .61x = 163.59

-.41x = - 11.48

x = 28 liters of 20%      287-28 = 259 liters of 61%

.....and please realize, these are made up numbers for your question....don't believe the temps have gone up quite that much:

"For example, the average annual temperature for the globe between 1951 and 1980 was around 57.2 degrees Fahrenheit (14 degrees Celsius). In 2015, the hottest year on record, the temperature was about 1.8 degrees F (1 degree C) warmer than the 1951–1980 base period."

13x = 0.5   divide both sides by 13

13x /13 = .05/13

x = .05/13 = 0.0038461538461538

I think you'll need to use the ACTUAL  KELVIN degrees (not just the absolute value of the increase) to calculate the PERCENTAGE increases of temperature over the years. (actual temps not given in question)

1.85% x 50 years = would be a 93 % increase in temperature !

2.5 F degree s / 50 years = .2.5/50 = 0.05 degrees F per year

390#  /  26# / yr   =  390/26  yr = 15 yrs

I think the formula you need  is:

A = P( i (1+i)^n / ((1+i)^n-1)    A = monthly payment   n = 12 payments   i = periodic interest in decimal = 19.5/12=.01625

A= 6927 (.01625 (1.01625)^12/  (1.01625)^12  -1)

A=640.02    each month for 12 months

- .52x  + .32 x = 4.6

-.2x = 4.6

x = 4.6/(-.2)

x = - 23