01 : ANSWER
In Mathematics, we use Order of Operations "PEMDAS" (Parentheses, Exponents, Multiplication/Division, Addition/Subtraction)
When we solve any mathematical equation, we first solve Multiplication/Division and then we solve Addition/Subtraction,
hence when we multiply 5X2 = 10 and then 10+5 = 15,
so the final answer is 15.
02 : ANSWER
X is 1.
The sides of the triangle are 3, 5, 8.
Since 3+5 = 8, this triangle is "degenerate", i.e., it collapses into a straight line.
About 10% of people catch this and conclude that X must be 0. But that's the wrong anwer!
The right answer is that X=1, so the left most triangle is degenerate 1, 4, 5 triangle, and the right most triangle is degenerate 1, 3, 4 triangle.