Text Formatting ⇒ How to align properly?

[ghostanime2001]

How can I remove the extra whitespace to the left of a) and b) so that is aligned with the red line ?

Here is my code:

Code: Select all

\documentclass[fleqn]{article}
\usepackage{fullpage}
\usepackage[inline]{enumitem}
\usepackage[margin=1in]{geometry}
\usepackage{graphicx}
\usepackage[parfill]{parskip}
\usepackage{mathtools}
\usepackage{amsmath}
\usepackage{siunitx}
\pagestyle{empty}
\renewcommand{\labelenumi}{\arabic{enumi}.}
\renewcommand{\labelenumii}{\alph{enumii})}
\newcommand{\la}{\lambda}
\setlength{\mathindent}{0in}
\setlength{\parindent}{0in}
\setlength{\parskip}{0in}
\everymath{\displaystyle}
\begin{document}
\begin{enumerate}[leftmargin=0in]
\item
$\begin{aligned}[t]
&\la=\text{0.5 m} \\
&f=\text{20 Hz}
\end{aligned}$
\qquad
$\begin{aligned}[t]
&v=\la f \\
&v=10
\end{aligned}$
\item
$\begin{aligned}[t]
&v=340 \\
&f=\text{1000 Hz}
\end{aligned}$
\qquad
$\begin{aligned}[t]
&\dfrac{v}{f}=\la \\
&0.34=\la
\end{aligned}$
\item
$\begin{aligned}[t]
y(x,t)=0.015\sin(25-1200t)
\end{aligned}$
\begin{enumerate}[leftmargin=*,labelsep=0cm,labelwidth=0cm,labelindent=0cm]
\item
$\begin{aligned}[t]
y(x,t)=0.015\sin(25-1200t)
\end{aligned}$
\item
$\begin{aligned}[t]
v=\la f
\end{aligned}$
\hspace{1.2in}
\smash{$\begin{aligned}[t]
&v=(0.25)(191) \\
&v=47.75 
\end{aligned}$}
\end{enumerate}
\begin{minipage}[t]{2in}
\vspace{0cm}
$\begin{aligned}[t]
&k=\dfrac{2\pi}{\la} \\
&\la k=2\pi \\
&\la=\dfrac{2\pi}{k} \\
&\la=\dfrac{2\pi}{25} \\
&\la=0.25
\end{aligned}$
\rlap{$\begin{aligned}[t]
&k=\dfrac{2\pi}{\la} \\
&\la k=2\pi \\
&\la=\dfrac{2\pi}{k} \\
&\la=\dfrac{2\pi}{25} \\
&\la=0.25
\end{aligned}$}
\end{minipage}
\end{enumerate}
\end{document}