Multiply both sides by d(m+p) to eliminate the denominator.

here's how to solve (a):

Step 1: Multiply both sides by $d(m+p)$ to eliminate the denominator. $h = \frac{mt}{d(m+p)}$ $hd(m+p) = mt$

Step 2: Expand the left side of the equation. $hdm + hdp = mt$

Step 3: Gather all terms containing $m$ on one side of the equation. $hdp = mt - hdm$

Step 4: Factor out $m$ from the terms on the right side. $hdp = m(t - hd)$

Step 5: Divide both sides by $(t - hd)$ to make $m$ the subject. $m = \frac{hdp}{t - hd}$

The final answer is $\boxed{m = \frac{hdp}{t - hd}}$.