Question

x^2 - 9x - 90 = 0, where x is her actual marks

Answer 1

Answer: 15

Step-by-step explanation:

$\mathsf{x^{2} -9x-90=0}$

$\mathsf{x^{2} -15x+6x-90=0}$

$\mathsf{x(x-15)+6(x-15)=0}$

$\mathsf{(x-15)(x+6)=0}$

$\mathsf{x=15,x=-6}$

As marks shouldn't be negative, x=15