We call the ratio between two directly proportional quantities the constant of proportionality. When these two quantities may increase or decrease, the constant proportionality always remains the same
So, let's make these two values improper fractions so they're easier to work with. 
So, to get the rate he grew in those months we have:
And to get the rate he grew in one month we have to divide both our numerator and our denominator by 21 to get:
aka he grew 1.24 inches in a month.
B= 60
To find b you must do the pythagorean theorem because it is a right triangle
65^2 - 25^2=b^2
3600=b^2
60=b
x= 18
To find x you must know that a triangle is made up of 180 degrees.
x= 180-(72+90)
x=180-162
x=18
hope this helped :)