`d)`
`(x^2 + 8x+7)(x+3)(x+5) + 15`
` = (x^2 + 8x + 7) (x^2 + 5x + 3x +15) +15`
` = (x^2 + 8x+7)(x^2 + 8x + 15) +15`
` = [ (x^2 + 8x + 11) - 4] . [ (x^2+ 8x+11) + 4] + 15`
` = (x^2 + 8x + 11)^2 - 4^2 + 15`
` = (x^2 + 8x + 11)^2 - 16 + 15`
` = (x^2+ 8x+11)^2-1`
` = (x^2 + 8x + 11)^2 - 1^2`
` = (x^2+ 8x+11-1)(x^2+8x+11+1)`
` = (x^2 + 8x+10)(x^2+8x+12)`
` = (x^2 + 8x + 10) ( x^2 + 2x + 6x + 12)`
` = (x^2 + 8x+10) [ x(x+2) + 6(x+2)]`
` = (x^2 + 8x+10)(x+6)(x+2)`
