Please help with this

Step-by-step explanation:

Given that,

In an AP, the 6th term is 39 i.e.

In the same AP, the 19th term is 7.8 i.e.

Subtract equation (1) from (2).

7.8 - 39 = a+18d - (a+5d)

-31.2 = a +18d-a-5d

-31.2 = 13d

d = -2.4

Put the value of d in equation (!).

39 = a+5(-2.4)

39 = a- 12

a = 39+12

a = 51

The sum of n terms of an AP is given by :

Put n = 25 and respected values,

Hence, the sum of first 25 terms of the AP is equal to 555.

hi,

you half the rectangle that you ae asking about so then you would see the scale factor of 1/2 the one u have selected, the one on top is half.

hope this !