По теореме синусов

AB/sin(∠C) = BC/sin(∠A) = AC/sin(∠B)

AB/sin(∠C) = 10/sin(45°) = 10√2

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BC/sin(∠A) = 10√2

BC = 10√2 * sin(60°) = 10√2 * √3/2 = 5√6

x = 5√6

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∠B = 180° - ∠A - ∠C = 180 - 60 - 45 = 75°

Понятна трудность, синус 75° :)

sin(75°)  = sin(45 + 30) = sin(45°)*cos(30°) + cos(45°)*sin(30°) = 1/√2 * (√3/2 + 1/2) = (√3 +1)/(2√2)

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AC/sin(∠B) = 10√2

AC =  10√2 * sin(∠B) = 10√2 * sin(75°) = 10√2 * (√3 +1)/(2√2) = 5(√3 + 1) = 5√3 + 5

y = 5√3 + 5