Verified answer

bn = b1 * q^(n-1) n-й член прогрессии

b4 - b2 = 24

b2 + b3 = 6

сложим

b4 - b2 + b3 + b2 = 24 + 6

b3 + b4 = 30

b2 + b3 = 6

b1*q^2 + b1*q^3 = q*(b1*q + b1*q^2) = 30 (1)

b1*q + b1*q^2 = 6 (2)

делим (1) на (2)

q*(b1*q + b1*q^2)/(b1*q + b1*q^2) = q = 5

5*b1 + 25*b1 = 6 подставляем в (2)

30*b1 = 6

b1 = 1/5

b4 = b1*q^3 = 1/5 * (5^3) = 25