Isolate the factor (s+t): s+t = q / (r/2). This simplifies to s+t=2q/r.
Subtract s from both sides to isolate t:
t=2q/r - s (Answer).
Alternatively, mult. both sides of q=(s+t)(r/2) by 2 to eliminate the fraction r/2:
2q=(s+t)(r) = sr + tr
Subtract sr from both sides: 2q - sr = tr
Divide both sides by r to obtain an equation for t: (2q/sr) - (sr/r) = t,
or (2q/sr) - s = t