How to get the length of 12 & a width of 5 then what is its perimeter?

Which of the fallowing best completes the sequence 5,10,15, a) 30 b) 22 c)25 d)35

The length of triangle base is 26. a line, which is parallel to the base divides the triangle into two equal area parts. find the length of the segment between triangle legs.

If the ratio of sum of the first m and n terms of an ap is m2 : n2 , show that the ratio of its mth and nth terms is (2m − 1) : (2n − 1).