7.8x - (3x + 1)(5x + 1)
= 7.8x - (15x^2 + 5x + 3x + 1)
= 7.8x - (15x^2 + 8x + 1)
= 7.8x - 15x^2 - 8x - 1
= -15x^2 - 0.2x - 1

(y+2)(y+3) - (y^2 + y)
= y^2 + 3y + 2y + 6 - y^2 - y
= y^2 + 5y + 6 - y^2 - y
= 4y + 6

(c+2)c + (c+3)(c-3)
= c^2 + 2c + c^2 - 9
= 2c^2 + 2c - 9