9. she spends 1 hour total and 1/2 hour on spanish. So she has another 1/2 on another subject ( as she spends equal time on each subject)
So number of subjects = 1 / 1/2 = 1 * 2 = 2
1. Write the equation:
d(-3 + x) = kx + 9
2. "Open" the parenthesizes:
-3d + dx = kx + 9
3. Take kx to the left side, -3d to the right, everything with different sign (+ replace with - when transferring, - replace with +):
dx - kx = 9 + 3d
4. Factor x in the left side:
x(d - k) = 9 + 3d
5. Finally, divide the whole equation by (d - k):
x = (9 + 3d)/(d - k)
That's the final answer. Good luck!
It looks like your first selection (a) is appropriate.
