Your guess was wrong, but the result works out to be exactly the same as the right answer.
From NFHS 9-1 Penalties... Start with 4b, which will lead you back to 3.
"3. If there is a simultaneous violation by each team, the ball becomes dead and no point can be scored. Remaining free throws are administered or play is resumed by the team entitled to the alternating-possession throwin from the designated out-of-bounds spot nearest to where the simultaneous violation occurred.
4. If there is a violation first by the free-thrower's opponent followed by the free thrower or a teammate:
b. If the second violation is by the free thrower or a teammate behind the free-throw line extended and the three-point line, both violations are penalized, as in penalty item (3)."