Yes, this is true. All squares are rectangles but no rectangles are squares. Squares and rectangles are classified as quadrilateral
The explicit formula for an arithmetic sequence is an = a1 + d(n - 1) where a1 is the first term and d = common difference. For this sequence a1 is 7 and d = 13- 7 = 19 - 13 = 25 - 19 = 6
So explicit formula required = 7 + 6(n - 1)
2. Boys to girls is 4/5 = 20/X
Cross multiply 4x= 100 X= 25 girls
3. 20/45= 4/9