The mass in grams of melons from market gardener B is modelled by a random variable $M_\mathrm{B}$ that follows a normal distribution with mean 1050 and unknown standard deviation $\sigma$. Melons are described as ``compliant'' if their mass is between 900 g and 1200 g.\\
The retailer observes that $85\%$ of melons supplied by market gardener B are compliant. Determine the standard deviation $\sigma$ of the random variable $M_\mathrm{B}$. Give the value rounded to the nearest integer.