[tex]the\ current\ mortage\ rate\ is\ 10.0\%\\\\the\ value\ of\ mortgage\ is\ \$90,000+10\%\cdot\$90,000=\$99,000\\\\the\ required\ down\ payment\ 15\%:\\\\\ \ \rightarrow\ \ 15\%\ of\ \$99,000=0.15\cdot\$99,000=\$14,850\\\\ the\ total\ monthly\ payment\ for\ a\ 30\ year\ loan:\\\\ \frac{\big{\$99,000-\$14,850}}{\big{30\cdot12}} =\frac{\big{\$84,150}}{\big{30\cdot12}} =\$233.75[/tex]
