(4.2x−1.2y)÷0.06−1.2x+6.7y help plz

Which of the following is missing in the explicit formula for the compound interest geometric sequence below?

Idon't get undoing if its pass adding and subtracting so can someone ? x-2 over 5 = 18

(c) a vine called the mile-a-minute weed is known for growing at a very fast rate. it can grow up to 0.5 ft per day. how fast in inches per hour can the mile-a-minute weed grow up to? show your work using the correct conversion factors.