Well 50°F is 10°C and every 9°F is 5°C so 45°F is 10 - 5(5/9), which is (10° - 2.78°)C, or 7.22°C
And 50 + (9/5)(45-10°C) is 50 + 35*9/5, which is 50 + 315/5, which is 50+63°F = 113°F
But a simpler way to do the second one is to just happen to know that 30°C is 86°F and 35°C is 95°F and 40°C is 104°F and since every 9°F is every 5°C, 45°C must be 104+9 = 113
I may have had a little too much fun with temperature calculating when I was little