b=?

Solve for b:
7.15 = 780.42 b

7.15 = 780.42 b is equivalent to 780.42 b = 7.15:
780.42 b = 7.15

Divide both sides of 780.42 b = 7.15 by 780.42:
(780.42 b)/780.42 = 7.15/780.42

780.42/780.42 = 1:
b = 7.15/780.42

7.15/780.42  =  0.00916174:
Answer: |  b = 0.00916174

\(\color{red}7.150=0.84b+13.77e^{-0.25b}\)

Use Wolfram Alpha for these kind of so-called difficult equation. This may be made up by your friend who wants to trick you and themselves cannot solve this neither.

\(\color{red}b = \frac{1}{84} (336 W_n(\frac{-459}{(112 e^{(\frac{715}{336})})}))\)

Wow. There came the perfect answer from Wolfram......