The shapes are similar.
When two figures are similar, the ratios of the lengths of their corresponding sides are equal.
Therefore,
[tex] \frac{42}{(15 + 42)} = \frac{x}{10 + x} [/tex]
Simplify:
[tex] \frac{42}{57} = \frac{x}{10 + x} [/tex]
Cross multiply:
42(10+x) = 57x
420 + 42x = 57x
420 = 57x - 42x
420 = 15x
x = (420÷15)
x = 28
