Call:
lm(formula = y ~ x)

Residuals:
      Min        1Q    Median        3Q       Max 
-0.087762 -0.021962 -0.003595  0.004626  0.237933 

Coefficients:
                      Estimate Std. Error t value           Pr(>|t|)    
(Intercept)           0.003611   0.005667   0.637             0.5250    
xLow income           0.084179   0.010165   8.281 0.0000000000000763 ***
xLower middle income  0.048468   0.008810   5.502 0.0000001672937218 ***
xNA                  -0.003595   0.040865  -0.088             0.9300    
xUpper middle income  0.018376   0.008673   2.119             0.0358 *  
---
Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1

Residual standard error: 0.04047 on 144 degrees of freedom
Multiple R-squared:  0.3587,	Adjusted R-squared:  0.3408 
F-statistic: 20.13 on 4 and 144 DF,  p-value: 0.0000000000003461