We can use ratios, in other words, if one part of the photo is changed x times, how many times does the other part change?
We can set up the proportion as :
width 1 : length 1 = width 2 : length 2
20 : 30 = 5 : x
We do inverse multiplication, or multiply the outer with outer and inner with inner (W1 * L2 and L1 * W2)
20*x = 30*5
20x = 150
Divide all by 10
2x = 15
Divide all by 2 to isolate x
x = 15/2
x = 7.5cm
