A fruit and vegetable retailer buys melons from market gardener A. The mass in grams of melons from market gardener A is modelled by a random variable $M_\mathrm{A}$ that follows a uniform distribution on the interval $[850; x]$, where $x$ is a real number greater than 1200. Melons are described as ``compliant'' if their mass is between 900 g and 1200 g. The retailer observes that $75\%$ of melons from market gardener A are compliant. Determine $x$.

Let $X$ denote a random variable following the uniform distribution on $\left[ 0 ; \frac { \pi } { 2 } \right]$. The probability that a value taken by the random variable $X$ is a solution to the inequality $\cos x > \frac { 1 } { 2 }$ is equal to:
Answer A: $\frac { 2 } { 3 } \quad$ Answer B: $\frac { 1 } { 3 } \quad$ Answer C: $\frac { 1 } { 2 } \quad$ Answer D: $\frac { 1 } { \pi }$

A company's shuttle bus departs at 7:30, 8:00, and 8:30. Xiaoming arrives at the bus station between 7:50 and 8:30 to board the shuttle, and his arrival time is random. The probability that his waiting time does not exceed 10 minutes is
(A) $\frac { 1 } { 3 }$
(B) $\frac { 1 } { 2 }$
(C) $\frac { 2 } { 3 }$
(D) $\frac { 3 } { 4 }$