Question

Solve for t q=(s+t)(r/2)

Answer 1

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