Start with

Multiply both sides by 5:

3rd - 25 is the 3rd term in the sequence
Answer:
924m^3 is the volume of the rectangular prism
9x^2+t+25=(ax+b)^2
9x^2+t+25=a^2*x^2+2abx+b^2 so
a^2=9 so a=3
b^2=25 so b=5 then
t=2ab using a and b from above
t=2*3*5=30
So the missing term is 30x