Hi there,
Z = Ma = ba
You made a typo. One of those = signs should either
be a + and a -. Here are all possibilities:
1. Z+Ma = ba, solve for a
Ma-Ba = -Z
a(M-B) = -Z
a = -Z/(M-B)
2. Z = Ma+ba, solve for a
Ma+ba = Z
a(M+b) = Z
a = Z/(M+b)
3. Z-Ma = ba, solve for a
Z = Ma+ba
Ma+ba = Z
a(M+b) = Z
a = Z/(M+b)
4. Z = Ma-ba, solve for a
Ma-ba = Z
a(M-b) = Z
a = Z/(M-b)
Hope it helps.