HELP PLEASE A

  last choice

In general if we have first term a[1] and common difference d, such that

a[n] = a[n-1] + d

then the explicit formula is

a[n] = a[1] + d(n-1)

First choice has d=-4 so needs a minus sign in the explicit formula.

Second choice has a=-100 so needs a negative sign for the 100.

Third choice swaps a[1] and d, oops.

36 girls

step-by-step explanation:

the 48 boys is 4 parts of the ratio

divide 48 by 4 to obtain one part of the ratio

= 12 ← 1 part of the ratio

3 parts = 3 × 12 = 36 ← number of girls